A rotation restricting mechanism comprising a rotation-restricting-mechanism-rotating-body ; and a fixed restricting member configured to engage with the rotation-restricting-mechanism-rotating-body by moving in a rotation axis direction of the rotation-restricting-mechanism-rotating-body and restrict rotation of the rotation-restricting-mechanism-rotating-body , wherein the rotation-restricting-mechanism-rotating-body comprises: a plurality of beam-like radial-support parts extending in a radial direction in a radial pattern, inner end portions of the radial-support parts being configured to be connected to a rotator to rotate integrally with the rotator , the inner end portion of each of the radial-support parts being located at an inner end in the radial direction of the radial-support part ; a plurality of beam-like first-circumferential-connecting parts connecting the inner end portions of the radial-support parts that are mutually adjacent; a plurality of beam-like second-circumferential-connecting parts connecting outer end portions of the radial-support parts that are mutually adjacent, to thereby form a polygonal shape, the outer end portion of each of the radial-support parts being located at an outer end in the radial direction of the radial-support part ; and a plurality of engaging protrusions , each of the engaging protrusions extending outwardly in the radial direction from the outer end portion of each of the radial-support parts , wherein in a state where the fixed restricting member is located so as to overlap the engaging protrusion when viewed in a direction orthogonal to the axial direction, an interval between the engaging protrusions that are mutually adjacent in a circumferential direction out of the plurality of engaging protrusions has a distance that enables relative movement of the fixed restricting member in the circumferential direction between the adjacent engaging protrusions . a plurality of beam-like radial-support parts extending in a radial direction in a radial pattern, inner end portions of the radial-support parts being configured to be connected to a rotator to rotate integrally with the rotator , the inner end portion of each of the radial-support parts being located at an inner end in the radial direction of the radial-support part ; a plurality of beam-like first-circumferential-connecting parts connecting the inner end portions of the radial-support parts that are mutually adjacent; a plurality of beam-like second-circumferential-connecting parts connecting outer end portions of the radial-support parts that are mutually adjacent, to thereby form a polygonal shape, the outer end portion of each of the radial-support parts being located at an outer end in the radial direction of the radial-support part ; and a plurality of engaging protrusions , each of the engaging protrusions extending outwardly in the radial direction from the outer end portion of each of the radial-support parts , wherein in a state where the fixed restricting member is located so as to overlap the engaging protrusion when viewed in a direction orthogonal to the axial direction, an interval between the engaging protrusions that are mutually adjacent in a circumferential direction out of the plurality of engaging protrusions has a distance that enables relative movement of the fixed restricting member in the circumferential direction between the adjacent engaging protrusions . <EOS>