The robbers attacked a 30-year-old employee who was forced to collect money from a machine for the suspects, police said.
The employee's right hand was cut during the incident.
The Yomiuri Shimbun said the suspects dropped about half of the money as they fled from the scene Saturday.
The Yomiuri Shimbun said the assailants, who have not been caught, were wearing caps and masks.
More than 400 customers were at the Kitakyushu parlor at the time of the robbery, police said.