PURPOSE: To prevent judgement error to the utmost by quickly and correctly performing an inspection work for a firing signal to a gate of a triode AC switch by a simple check means such as a tester or the like.

CONSTITUTION: A commercial A, C power is supplied to a motor 4 by a triode AC switch 6 or 7. The triode AC switches 6, 7 becomes conducting when a pulse firing signal is given from a control circuit 1 to a gate in the normal washing operation. When a check mode is set by specially operating a key switch of a console panel, the triode AC switches 6, 7 conduct as a D.C. continuous firing signal is given from the control circuit 1 to the gate. An inspection operator can check a continuous firing signal from the control circuit 1 by a simple checking means such as a tester or the like quickly and correctly so as to prevent judgement error to the utmost.