A core (10) comprises a plurality of core split members (11) having yoke portions (22) and tooth portions (21) and arranged in such a circumferential shape that the yoke portions (22) contact with each other while the tooth portions (21) being directed inward. The core (10) further comprises a ring (12) contacting with the yoke portions (22), and stoppers (13) mounted on the outer face sides of the yoke portions (22) for fixing the ring (12) on the yoke portions (22). The yoke portions (22) and the ring (12) are formed with corrugations to mesh with each other, and the stoppers (13) are formed with projections to be caught from the inner side by the ring (12). This structure provides both the rotary motor core having the core split members arranged in the circumferential shape and fastened to each other while preventing occurrence of a stress and a positional displacement between the cores, and a rotary motor.