PURPOSE: To prevent the generation of the cracking in an exposed mask when the mask is automatically washed in unattended operation, by confirming the complete setting of the exposed mask on a stage with set confirming sensors.

CONSTITUTION: An exposed mask 2 is clamped with a robot hand and set on the stage of a washing machine. Then, detecting pins 9a of four divided stage tables 1A, 1C and the like of the stage are protruded by a specified amount. Said protrusions are detected by metallic approach sensors 9b of confirming sensors 9, which are provided at corresponding positions. Thus the complete setting of the mask 2 is confirmed. The washing of the mask 2 is automatically started. In this way, yield of cracking of the exposed mask due to incomplete setting at the time of unattended automatic washing operation is prevented.