With all the debate over a possible constitutional revision in Japan aiming towards formal remilitarization (of course their informal military is already among the world’s best equipped), there have been quite a few mentions of how Japan’s current constitution is so limiting that it actually blocks Japan from collaborating with the US in constructing a missile defense shield in Japan. This is supposedly due to Japan’s ban on the export of arms, so you might be forgiven for actually believing that Japan doesn’t sell weapons to other countries. This article at Asia Times (originally from Japan Focus) explains the technicalities and blurry definitions that the Japanese government exploits to enable a continuation of their claim that they do not trade in weapons, while still being able to profit by selling small arms all around the world.
Japan actually conducts a thriving small arms export trade. The international annual publication, the Small Arms Survey, for example, reported that in 2002 Japan exported $65 million worth of small arms which, in monetary terms, ranks Japan among the top eight exporters of small arms worldwide for that year. 
The Japanese government evades this issue by contending that “hunting guns and sport guns are not regarded as ‘arms’,”  and therefore the self-imposed ban on arms exports only applies to guns of a military specification. This raises the question of what differentiates a military specification gun from a sporting or hunting weapon. However, the Japanese Ministry for Export, Trade and Industry (METI) provides no comprehensive definition. Instead it decides on a case-by-case basis whether a weapon should be defined as being of military specification.
This is another example of saying one thing and doing another, much in the same vein as the policy of promoting commercial whaling in the guise of “science” while still being party to a treaty outlawing commercial whaling, as I discussed a few days ago. Unlike the whaling hypocrisy, the open secret of Japan’s international weapons trade seems to have remained completely beneath the radar. While I have in the past been slightly confused by references I’ve seen to Japan-manufactured guns, until I saw this article I just shook off the momentary bafflement without realizing the actual situation. A highly recommended read.