Disclosed herein is a PM type step motor used to move a camera or an optical pickup lens of media related equipment. In the step motor, coupling holes are formed in the central portions of both sides of a casing unit thereof, a bushing is press-fitted or inserted into an associated coupling hole, and a ring member is press-fitted over the outer circumference of the bushing protruding outward from the coupling hole such that the bushing is secured to the casing unit, thus preventing the bushing from becoming separated from the casing unit. The step motor can be freely applied to peripheral device modules of various outer diameters using the ring member.