Two vending machines at the Marunouchi Line's subway stop in Tokyo's Shinjuku Station are dispensing free chocolate and attracting swarms of customers ahead of Valentine's Day.

Distributing only Yuraku Confectionery Co.'s canned Black Thunder chocolate bars, which normally cost ¥30, they have been dubbed "giri choco" machines after the inexpensive chocolates Japanese women present their male counterparts Feb. 14 out of a sense of social obligation.

The cans of chocolate have become a widely popular Valentine's Day gift since the firm started selling them in 1994.

In addition to gifting their loved ones chocolates on Valentine's Day, many women at schools and offices feel obliged to give small inexpensive chocolates to their male colleagues, bosses or friends.

This year, Yuraku Confectionery is distributing the free Black Thunder bars, at three per can and one to a customer, via the machines, hoping to promote giri choko culture in a week-long Valentine's Day campaign that began Monday. The company is distributing 1,000 of the promotional cans every day through Sunday, starting at noon.

Long lines have formed every day in front of the machines.

Riku Tachikawa, 16, who visited Shinjuku Station on Saturday with his friend, Kaname Kohama, also 16, said: "We came to line up at 9 a.m. this morning. We probably won't receive any chocolate on Valentine's Day as we attend boys' only schools, so we came to get some here. I was also interested in checking out the vending machines."

A woman who also came for the free sweets said she plans to give one to her father. Asked what she will give her boyfriend Feb. 14, she replied, "I plan to make some chocolate for him."