PURPOSE: To enable the judging of a trouble in an agitation blade drive system accurately in a short time by counting the pulses representing the number of revolutions detected of a motor for a motor-ON period and a motor-OFF period separately to compare the number of pulses during a specified OFF period with a specified value.

CONSTITUTION: Washing is put into a washing tank 2 and when a start switch is closed, bidirectional thyristors 7a and 7b at a motor drive section 7 open or close alternately based on a drive command of a motor control section 10d at a controller 10 so that a motor 5 is rotated clockwise and counterclockwise to rotate an agitation blade 3 through a decelerator 4. At this point, the number of revolutions of the motor 5 affected by the washing is detected with a number of revolutions-detecting section 8 to count pulses during an OFF period within a specified term with a counter section 10a. Then, the number of pulses N during the OFF period is compared with the number of pulses X1 prepared as such for detecting abnormality by a cloth quantity judging section 10b, and when N>X1, an agitation blade drive system is determined to break down. A motor power source is turned OFF immediately with the motor control section 10d.