Jinbocho in Tokyo's Chiyoda Ward is Japan's treasure trove of used books.

Visitors there can be divided at least into two classes.

One of those will have fairly fat wallets and go inside bookstores to seek out and buy normally priced old books.

The other denizens of this bookworms' wonderland are tight-fisted types who do not look at the shelves inside the shops, but instead sift through piles of 100 yen books on stands outside in search of a special snip.

This writer, who is undoubtedly from the latter class, has long panned these 100 yen streams in search of printed gold dust -- but his wife doesn't quite see it that way. "Don't bring any more of your Jinbocho books into our small apartment" is how she delicately puts it.

Eternally optimistic

Little does she know that there's an even lower class of book-browser there -- one with a raptor's eyes for signs on boxes in the street reading: "Gojiyu ni dozo (Take these freely)." Upon spotting this sign, such types -- likely including those under orders to bring back no more 100 yen books -- will swoop on the hoard of shop-owners' castoffs, eternally optimistic of finding an overlooked gem.

From one such box, this writer will never forget the time he retrieved a 1932 Japanese translation of a 1906 German book on historical Jesus. It is a tome of less than general appeal, perchance -- but one that continues to fuel the scavenging urge within.

There is, though, an even lower subspecies of Homo jinbocho. This one, crow-like, stalks the streets in search of books whose last resting place has become the pavement itself. So it was, the other day, that this shameless sort spied a small book lying there discarded -- and popped it in his pocket.

Eureka! Jinbocho's wonders never cease: That printed "litter" turned out to be the second volume of a 1949 Japanese translation of Giovanni Boccaccio's "Decameron." Now a rare book, this contains a portrait of the author, four photogravure pages of detailed etchings and woodblock prints at the start of each story. A true find indeed.

Meanwhile, in total contrast, this stingy Jinbocho regular was recently privileged to join a tour of the usually locked second or third-floor "treasure" rooms of some bookstores there.

The tour, taken with Ann Herring, professor of the history of publishing culture at Hosei University as a special guide, was organized by the National Institute of Informatics for its foreign students who, a PR type explained, "may spend too much time gazing at computer screens to be sufficiently exposed to Japanese culture."

The tour did nothing but confirm notions of the treasures hidden there, with items shown at one shop, Yagi Shoten, including:

* One of the 1 million wooden stupas containing a sutra that the female Emperor Shotoku (reigned 764-770) gave to the 10 major Buddhist temples in and around the ancient capital of Nara to pray for peace. With the sutras now believed to be the world's oldest printed matter, a stupa containing one will set you back around 7.5 million yen.

* An illustrated, 17th-century copy of "Taketori Monogatari (Bamboo Cutter)," Japan's earliest prose romance from the Heian Period, going for 9.8 million yen.

Down the road at Isseido Shoten, however, was where some price tags took an exponential turn, with two items beheld there being particularly rare:

* An astrological calendar of the year of 1215 from the Kofuku-ji Temple in Nara, with diary-like entries of what happened each day. Price: 28 million yen.

* A copy of Confucius's "Analects" in Chinese. Published in 1533 by a doctor in Osaka, it is Japan's second-oldest copy of that title. Price: 12 million yen.

Amazingly, Takehiko Sakai, an Isseido Shoten executive, said to the group: "Don't hesitate. You can touch these items freely."

Culturally fascinating

Next stop on the tour was the second (unlocked) floor of Subun-so Shoten, where manager Noriaki Abe showed us some less expensive (around 150,000 yen) but culturally fascinating items called chirimen bon (literally, "silk-crepe books").

This genre of crepe-paper books are typically Japanese fairy tales rendered in a European language -- usually English, German, French and even Danish -- and bearing fine illustrations. Dating from around 1885, these were used at middle schools as foreign-language skill books, but soon also became prized souvenirs for foreigners in newly opened Japan to send or take home.

Finally, the tour took in Rama-sha, a store where more recent items were displayed. These included a mimeographed script for the first "Godzilla" movie, titled "G Sakuhin (G Work)" and priced at 600,000 yen. There was, too, a copy of photographer Nobuyoshi Ara- ki's first photo book showing scenes from his honeymoon. Titled "Sentimental Journey," only 1,000 copies of this were published privately in 1971 -- and now one can be yours in Jinbocho for a mere 450,000 yen.

If these special rooms in some Jinbocho bookstores are like museums, some Jinbocho booksellers are as knowledgeable as the best-informed curators.

Living proof of this was Kimio Koketsu, president of Ohya Shobo, which specializes in woodblock prints, old maps and Edo Period books. He said: "With so many books coming to us, we hardly have time to sleep because we have to study so much."

Other than joining a tour, though, if you want to become an upper class Jinbocho bibliophile and be granted access to the stores' inner sanctums, the first thing to do is kick that scavenging or 100 yen habit. Then, armed with acquired knowledge or insatiably intelligent curiosity, you must venture inside numerous times to make the acquaintance of those working there.

If that doesn't yield an invitation upstairs . . . then Plan B may sadly require a serious investment to be made.