A stator, being formed in a tube shape, and the stator comprising: a coil; an insulation member; and a stator core comprising a plurality of salient pole parts, the coil being wound around each of the plurality of the salient pole parts through the insulation member; wherein the stator core comprises: an outer peripheral ring part which is formed in a ring shape; and the plurality of the salient pole parts which are protruded from the outer peripheral ring part to an inner side in a radial direction of the stator and are disposed at regular intervals in a circumferential direction of the stator; wherein the outer peripheral ring part is structured with a same number of outer peripheral parts as a number of the plurality of the salient pole parts; wherein each of a plurality of the outer peripheral parts is connected with one of the salient pole parts and each salient pole part is formed at a center of an outer peripheral part in the circumferential direction; wherein when an outer side face of an outer peripheral part in the radial direction is referred to as an outer peripheral face, both end side portions in the circumferential direction of the outer peripheral face of one of the outer peripheral parts are respectively formed to be a curved face part in a convex curved face shape which is a circular arc shape, said curved face parts have a same curvature radii and their curvature centers are common when viewed in an axial direction of the stator; and wherein an outer diameter of a portion between two of the curved face parts in the circumferential direction of the outer peripheral face of one of the outer peripheral parts is set to be smaller than an outer diameter of the curved face parts; the stator being characterized in that, the outer peripheral face of one of the outer peripheral parts is formed with a second curved face part in a convex curved face shape, which is a circular arc shape when viewed in the axial direction and is located between two of the curved face parts in the circumferential direction. a coil; an insulation member; and a stator core comprising a plurality of salient pole parts, the coil being wound around each of the plurality of the salient pole parts through the insulation member; wherein the stator core comprises: an outer peripheral ring part which is formed in a ring shape; and the plurality of the salient pole parts which are protruded from the outer peripheral ring part to an inner side in a radial direction of the stator and are disposed at regular intervals in a circumferential direction of the stator; an outer peripheral ring part which is formed in a ring shape; and the plurality of the salient pole parts which are protruded from the outer peripheral ring part to an inner side in a radial direction of the stator and are disposed at regular intervals in a circumferential direction of the stator; wherein the outer peripheral ring part is structured with a same number of outer peripheral parts as a number of the plurality of the salient pole parts; wherein each of a plurality of the outer peripheral parts is connected with one of the salient pole parts and each salient pole part is formed at a center of an outer peripheral part in the circumferential direction; wherein when an outer side face of an outer peripheral part in the radial direction is referred to as an outer peripheral face, both end side portions in the circumferential direction of the outer peripheral face of one of the outer peripheral parts are respectively formed to be a curved face part in a convex curved face shape which is a circular arc shape, said curved face parts have a same curvature radii and their curvature centers are common when viewed in an axial direction of the stator; and wherein an outer diameter of a portion between two of the curved face parts in the circumferential direction of the outer peripheral face of one of the outer peripheral parts is set to be smaller than an outer diameter of the curved face parts; the stator being characterized in that, the outer peripheral face of one of the outer peripheral parts is formed with a second curved face part in a convex curved face shape, which is a circular arc shape when viewed in the axial direction and is located between two of the curved face parts in the circumferential direction.