Here is a short article of the Economist summarising the economic importance of pachinko parlours in Japan.

The Economist : Pachinko - Rules of the game

Although casino-style gambling is illegal in Japan, pachinko slots are tolerated because they do not reward winners with money, but prizes (that end up being exchanged for money in back alleys). Pachinko gambling is an industry worth 30 trillion yen a year in Japan - more than the car industry ! It is similar to the status of prostitution, also officially illegal, but tolerated under the camouflaged form of soap lands and "massage" parlours. The sex industry in Japan is said to be worth even more than pachinkos.

The interesting part of the article is that it mentions that the pachinko industry is controlled mostly by Japan-born Koreans, and that part of the 30 trillion yen it generates is thought to be diverted to North Korea. I suppose that it is to support relatives, but it could as well be to keep Kim Jong Il on his feet... Ironic, isn't it ?