PURPOSE: To measure easily the pressing force of a blade by making it possible to set a blade pressing force measuring jig instead of a rotary drum of an electrostatic copying machine and allowing a cleaning blade in an action position to act upon a member to be detected.

CONSTITUTION: First, a rotary drum 28 is detached from a drum supporting unit frame in the copying machine body. Next, a blade pressing force measuring jig 2 is set to the supporting unit frame. Then, a supporting member of a jig body 4 is supported on the bottom wall of a receiving part, and a detaining means provided on an end plate is positioned in a notch formed in one side wall, and the jig body is set between side walls. At this time, the blade pressing force measuring jig 2 is set correctly, and the front end of a cleaning blade 30 placed in a non-action position is brought into contact with a face 16a to be contacted of a member 16 to be detected which is set to the jig body 2, and a solenoid 53 is excited to press the cleaning blade 30, and thereby, the quantity of displacement of the member 16 to be detected is measured, thus detecting the pressing force of the cleaning blade 30.