On Saturday, officers took dealer Keiji Oura, 32, and two other suspects into custody for providing poker in violation of gambling regulations.
Gambling on horse, motor boat, bicycle, and motorcycle racing from authorized betting outlets is legal in Japan.
The parlor, located inside a one-room residence in the Kita Shinagawa area, operated late at night. Seven male customers inside the residence at the time of the raid were also arrested.
All of the suspects have reportedly admitted to the allegations.
Law enforcement is attempting to determine if the casino was being as a source of funds for organized crime.
