To provide an inter-member juncture structure which allows the shortening the axial length of the inter-member juncture and the attachment and detachment between the members with one operation.

A hand piece body is provided with an insert part having a groove and a motor case is provided with a shaft hole 21 to accept the insert part. A ring member 22 having a chamfered part, a spring 25 and a pushing knob 26 are disposed in the shaft hole. The spring 25 energizes and shifts the ring member 22 to a offcenter position to offcenter the ring member from the concentric position concentric with the shaft hole. When the insert part is inserted into the shaft hole, the front end of the insert part comes into contact with the chamfered part of the ring member and the ring member 22 is displaced to the concentric position by overcoming the energization of the opring 25. When the groove appears on the inner side of the ring member 22, the ring member 22 is automatically reset to the offcenter position and the projecting part on the inner side of the ring member fits to the groove. A hand piece body and the motor case are connected by the fitting and are disconnected by the pushing knob 26.