An object is to detect the pressing force of a tip driven unit. In the controller 22, a motor control circuit 85, a load change detection unit 86, a moving speed calculation unit 87 that calculates the moving speed of a rotating body 41, a pressing force detection unit 88 that obtains the pressing force of the rotating body 41 based on the moving speed which is calculated, a CPU 89, and an alarm 91 are disposed. The pressing force is obtained based on the cycle of load change by the joint 41a in which a front end and a rear end overlap with each other is formed in the rotating body 41.
