Second, according to Article 62 of the Constitution, each House of the Japanese parliament (the Diet) may conduct investigations in relation to the government, including with respect to the lawfulness of information collection by the police. To that end, it may demand the presence and testimony of witnesses, and/or the production of records. Those powers of inquiry are further specified in the Diet Law, in particular Chapter XII. In particular, Article 104 of the Diet Law provides that the Cabinet, public agencies and other parts of the government "must comply with the requests of a House or any of its Committees for the production of reports and records necessary for consideration of investigation." Refusal to comply is allowed only if the government provides a plausible reason found acceptable by the Diet, or upon issuance of a formal declaration that the production of the reports or records would be "gravely detrimental to the national interest" (106). In addition, Diet members may ask written questions to the Cabinet (Articles 74, 75 of the Diet Law), and in the past such "written inquiries" have also addressed the handling of personal information by the administration (107). The Diet's role in supervising the executive is supported by reporting obligations, for instance pursuant to Article 29 of the Wiretapping Act.

Third, also within the executive branch the Prefectural Police is subject to independent oversight. That includes in particular the Prefectural Public Safety Commissions established at prefectural level to ensure democratic administration and political neutrality of the police (108). These commissions are composed of members appointed by the Prefectural Governor with the consent of the Prefectural Assembly (from among citizens with no public servant position in the police in the five preceding years) and have a secure term of office (in particular only dismissal for good cause) (109). According to the information received, they are not subject to instructions, and thus can be considered as fully independent (110). As regards the tasks and powers of the Prefectural Public Safety Commissions, pursuant to Article 38(3) in conjunction with Articles 2 and 36(2) of the Police Law they are responsible for "the protection of [the] rights and freedom of an individual". To this effect, they are empowered to “supervise” (111) all investigatory activities of the Prefectural Police, including the collection of personal data. Notably, the commissions "may direct the [P]refectural [P]olice in detail or in a specific individual case of inspection of police personnel's misconduct, if necessary" (112). When the Chief of the Prefectural Police (113) receives such a direction or by him-/herself becomes aware of a possible case of misconduct (including the violation of laws or other neglect of duties), (s)he has to promptly inspect the case and report the inspection result to the Prefectural Public Safety Commission (Article 56(3) of the Police Law). Where the latter considers this necessary, it may also designate one of its members to review the status of implementation. The process continues until the Prefectural Public Safety Commission is satisfied that the incident has been appropriately addressed.