Gambling in Japan is a curious blend of strict rules and surprising exceptions....

https://mag-wiki.win/index.php/Where_Do_I_Learn_Kyoutei_Rules_Before_I_Go%3F

Gambling in Japan is a curious blend of strict rules and surprising exceptions. While most forms are illegal, you can still try your luck at pachinko parlours, horse racing, keirin cycling, and kyoutei boat racing