To treat a drive section of a dental handpiece, such as high-pressure steam sterilization, reparately from a motor by constituting this drive section of a cylindrical motor case which freely insertably and removably houses its motor in an axial direction and a halting means for keeping the housed motor to halt in a prescribed position.

At the time of assembly of the drive section A, a motor body 2 is inserted into a motor housing hole 1a by placing a turning preventive bar 2d along a groove from the rear end of the motor case 1. This insertion is executed until the position where the front end face of a motor connector 2c and the rear end face 1b' of the thickness peripheral wall 1b of the motor case 1 come into contact. A cap 3 is thereafter mounted at the rear end of the motor case 1 and this motor body 2 is kept to stay put in the motor case 1. Namely, the projection on the cap 3 side is placed along an L-shaped notch 1g' and is pushed into the axial direction and is then turned in a circumferential direction, by which the cap is detained. At this time, the motor body 2 is made to stay put by means of the wave washer housed in the cap 3 without clattering.