To apply appropriate regular fastening force to screw parts of parts and equipment where the parts is mounted.

When a tip 11 is mounted to a hand piece 12, the tip 11 is inserted into a tip insertion hole 2a and a main body 1 is turned to a direction d. When frictional force of the screw parts of the tip 11 and the hand piece 12 becomes a specified force or more, a turning member 2 is started to be turned to a direction (a) while a turning force transmitting member 4 is started to be turned to a direction e, and a spring 5 is started to be expanded. When the turning force transmitting member 4 gets over a turning force transmitting part 3, mounting is completed. When the tip 11 is removed from the hand piece 12, the main body 1 is turned to a direction c. Though the turning force transmitting part 3 makes the turning force transmitting member 4 turn to a direction f by the frictional force of the screw parts of the tip 11 and the hand piece 12, the turning force transmitting member 4 is prevented from moving by a stopper 6, and turning force of the main body 1 to the direction c directly acts on the turning member turning member 2 as the turning force to the direction (a). The tip 11 is thereby started to be turned to a removing direction, and removed from the hand piece 12.