Gambling in Japan is a curious mix of strict laws and unique legal exceptions....

https://fast-wiki.win/index.php/How_to_Bet_on_Horse_Racing_in_Japan_as_a_Foreigner

Gambling in Japan is a curious mix of strict laws and unique legal exceptions. While most forms of gambling are illegal, you can still try your luck at pachinko parlours, horse racing, keirin (bicycle racing), and kyoutei (boat racing)