An electric motor comprises a motor case having a motor shaft and a gear case assembled with the motor case detachably. The motor shaft comprises a base end, an intermediate portion, and a remote end which are supported by the first, the second and the third bearing devices, respectively. The third bearing device has a slide bearing, a cap, an adjusting screw, and a lock nut. The adjusting screw stabilizes an axial clearance of the motor shaft. The slide bearing is engaged in a larger diameter bore of a shaft bore.