For American lawyers accustomed to struggling with massive walls of law books and expensive database services, one of the great things about Japanese law is that it is so compact and accessible.

In fact, most of what you will ever need to know fits into the roppō (六法), a small book containing a set of essential Japanese laws.

Roppō literally means “six laws” and originally referred to the six hōten (法典, codes) that are the foundation of Japanese law: the Kenpō (憲法, Constitution), Keihō (刑法, Penal Code), keijisoshōhō (刑事訴訟法, Code of Criminal Procedure), Minpō (民法, Civil Code), Minjisoshōhō (民事訴訟法, Code of Civil Procedure) and Shōhō (商法, Commercial Code). All have their roots in laws that were adopted during the Meiji Era (1868-1912) and are based on continental European models.

There have, of course, been some changes made to these six laws since they were adopted at the end of the 19th century and the beginning of the 20th. The constitution is no longer the Dainihon Teikoku Kenpō (大日本帝国憲法, The Constitution of the Empire of Japan), also commonly referred to as the Meiji Kenpō (明治憲法, Meiji Constitution), which was modeled on the Prussian Constitution and replaced in 1947 by the current American-influenced Nihonkoku Kenpō (日本国憲法, Constitution of Japan). A new Code of Criminal Procedure was adopted the following year to ensure the keijishihōseido (刑事司法制度, criminal justice system) matched the new Constitution. The current Code of Civil Procedure is newer still, having been adopted in 1996. In 2006, a big chunk of the Commercial Code was repealed and replaced with a separate Kaishahō (会社法, Company Act).

Another change is that, thankfully, most of these laws are no longer written in kanamajiribun (かな交じり文, text with kana), the kanji-heavy, punctuation-free text written using classical Japanese grammar that was once standard for statutes and official documents. The rendering of Japan’s laws into gendaigo or kōgotai (現代語 or 口語体, modern or colloquial) language that Japanese people can read easily has taken a surprisingly long time — conversion of the Civil Code was not completed until 2005. Nonetheless, some laws, including parts of the Commercial Code, are still written the old way, which can be a shock if you haven’t studied classical Japanese.

Japanese law has become more complex since the Meiji Era and roppō is also used to refer more broadly to six fields of law: constitutional law, including laws such as the Kokkaihō (国会法, Diet Act) and Naikakuhō (内閣法, Cabinet Act) that define government institutions; civil law (Minpō, meaning the Civil Code — as defined earlier — as well as countless other statutes that modify or replace its rules regarding contract, employment, tort, products liability and property); criminal law (Keihō, which refers to a myriad of statutes defining and punishing crimes, not just those in the Penal Code); Commercial Law (shōhō¸ the Commercial Code together with the Company Act and various other business-related statutes) as well as civil and criminal procedure, which refer to Minjisoshōhō and Keijisoshōhō again, but in this context they refer to other special procedural rules such as those governing shōnenjiken (少年事件, juvenile criminal cases) and hasanjiken (破産事, bankruptcy cases).

As noted at the outset, the roppō is a compilation of laws and a huge variety of these compilations exist. A student version costs less than ¥2,000 and contains the Constitution, the important codes and dozens of other laws and treaties (interestingly, the Peace Treaty of 1952 seems standard in even the most basic roppō). While hanreihō (判例法, case law) is not as important in Japan as it is in the U.S., hanrei (判例, court precedents) can still be important, so you might want to pay extra for a hanrei roppō (a roppō with case annotations).

Countless specialized roppō are also produced for people who work in regulated industries or government jobs. These may contain not only the more arcane hōrei (法令, laws and regulations) but the tsūtatsu (通達, official notices) that regulators use to conduct gyōseishidō (行政指導, administrative guidance). At various times in my own career as a lawyer I have carried around roppō for the railway, fisheries and telecommunications industries, so I could understand some of the legal issues affecting clients in Japan.

For those who want it all, Yuhikaku publishes the “Roppō Zensho” (六法全書, “Complete Laws”), an annual compilation of all Japanese laws currently in effect, conveniently packaged in two bricklike volumes. This compendium can be found cradled in the arms of junior lawyers at law firms around the nation. (You never know when you might suddenly need to look up the Anti-Human Cloning Act).

Of course most Japanese laws and regulations are now online, with a growing number available in English at the government’s Japanese Law Translation website (www.japaneselawtranslation.go.jp). Still, it’s just not the same as having it all in a handy, albeit thick, book.

In law, as in warfare, it occasionally helps to have something heavy to throw at the other side.

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