PURPOSE: To perform speedy inspection and recovery regarding the photosensitive drum of an electrophotographic copying machine, etc., only by inserting the measuring probe of a measuring instrument into a prescribed socket, and thus automatically insulating the photosensitive drum from the machine frame.

CONSTITUTION: A photosensitive drum 14 is grounded normally through supporters 13A and 13B, a center shaft 12, a bearing 11B, an electric conductor 16, a fitting screw 17, a contact spring 24, and a fixation-side contact 23. When a measuring probe A is inserted into a socket 20 for the inspection of a corona discharger 15, the contact spring and fixation-side contact are pressed to open at the tip part of the measuring probe, and the photosensitive drum 14 is ungrounded. Therefore, the measurement and recovery and performed only by inserting and extracting the measuring probe.