As in most Asian countries, Japanese diving is primarily done under the influence of the RSTC framework.
The RSTC, or WRSTC, stands for World Recreational Scuba Training Council, and is an organisation created in 1999 to establish common minimum recreational diving training standards for its affiliated scuba diving certification agencies.
Most of the affiliated agencies are North American-based, commercial associations such as PADI, SSI, SDI or NAUI, sharing unified training standards and certification levels (Open Water Diver, Advanced Open Water Diver, Rescue Diver, Divemaster etc…).

Looking at World Recreation Scuba Training Council (RSTC) affiliated agencies, PADI is the market leader – PADI Asia-Pacific’s Japan branch has issued more than 2 million certifications in the country since the first international office was established in Tōkyō in 1979, which gives it the second place for country with the most PADI-certified divers in the world.

NAUI is also quite represented in Japan, being the oldest RSTC agency established in the country (1970), and, as elsewhere in Asia, SSI dive-shop affiliations are on the rise, as is the SDI/TDI presence in the country (appreciated for its handy links to the TDI tech diving curriculum)

Japan also has a number CMAS affiliated diving federations, including:
the Japan-CMAS (JCS),
the CMAS Instructor Association Japan (JCIA),
the Japan Educational Facilities Federation  (JEFF),
the Kansai Sports Diving Federation Japan  (KD Japan),
the Marine Techno Educational System Diving Division  (MTES)

and the Japan Underwater Sports Federation  (JUSF), focussing on underwater sports activities.

Sharing similar standards to those of CMAS (of once it was once a member), the BSAC is also has an active presence in Japan.