When an abnormal washing condition occurs during a washing process, an auto-off power source switch is made automatically to present an off condition after a long shelf time such as one hour. In case of the abnormal washing condition of the washing process, since the switch maintains the long shelf time, an operator can notice such an abnormal condition during this long shelf time and then remaining normal washing process can be carried out continuously by getting rid of the abnormal cause. It is therefore unnecessary to re-set the washing process. After the washing process has been finished, the switch is made automatically to present the off condition at a short shelf time such as five minutes. During this short shelf time, it is unnecessary to start the switch at an on condition so as to re-start for carrying out next washing process.