Japan, unfortunately, has no overall privacy law. It is a patchwork of many kinds of laws, such as secrecy of communication protected by the Constitution, Act on the Protection of Personal Information, tort laws, Telecommunications Business Act, and other acts specific to certain industries.
In this case, the most relevant was Radio Law. "Nobody shall intercept wireless communication and leak the existence or contents of the communication, nor shall he make use of the information obtained by the interception of wireless communication." Article 59.
This, however, means that the act of intercepting itself is not illegal. According to Alan Eustace, Senior Vice President, Google never disclosed the information and it also has never intended to make use of the information. If it is true, it might be difficult to condemn Google's conduct as an illegal conduct. Of course, those whose privacy was invaded can file a lawsuit against Google by the theory of tort, as the victims do not know whether their own information was collected, this is not a realistic scenario.
What happened was that as Article 4 of the Telecommunications Business Act has a confidentiality clause, the Ministry of Internal Affairs and Communication rendered administrative guidance, saying that the conduct has the possibility to lead to the violation of the confidentiality clause.
But there are some problems on this logic. First, it is said that Google have not been reported itself as conducting telecommunications business (in Japan) according to the Telecommunications Business Act, because its servers are outside of Japan. Article 4 is only applicable to the telecommunications business. Second, at the time when Google's street view car collected privacy information, Google was not transmitting the information. Article 4 of the Telecommunications Business Act only prohibits the communication business "dealing with" communication from invading confidentiality of the communication. As Google's role was merely a "collector" of information and not a "transmitter" of information, it is unlikely (at least from the rigid interpretation of the text) that Google's act falls in the prohibition of Article 4 of the Act.
I believe that one of the reasons why there was no official administrative or criminal action against Google and just the guidance is that it was difficult to make a clear and convincing argument that Google violated administrative or criminal privacy laws.
This may call for the enactment of a wide privacy statute. Although the new statute can work very well, there is also the concern on undesirable consequences the statute may cause. Therefore, in order to make a good law which reconciles between privacy and other important values such as freedom of speech or access to information, I believe that further research on American or other foreign country's examples might be necessary.
DISCLAIMER: "IT Law issues in Japan" only provides general information about Japanese information technology law and does not, under any circumstances, constitute legal advice. You should first obtain the advice of professional legal counsel who is qualified in Japan before acting or refraining from acting based on this blog.