A stator, comprising: a coil; an insulation member; and a stator core provided with a plurality of salient pole parts around each of which the coil is wound through the insulation member; wherein the stator core is provided with an outer peripheral ring part formed in a ring shape and the plurality of the salient pole parts which are protruded from the outer peripheral ring part toward an inner side in a radial direction of the stator and are disposed at a constant interval in a circumferential direction of the stator; wherein the outer peripheral ring part is structured of outer peripheral parts having the same number as that of the plurality of the salient pole parts; wherein the outer peripheral parts are arranged in the circumferential direction and a center in the circumferential direction of each of the outer peripheral parts is connected with the salient pole part; wherein a joint is formed at one position of boundaries in the circumferential direction of the outer peripheral parts; wherein remaining positions of the boundaries in the circumferential direction of the outer peripheral parts except the joint are formed with connecting parts which connect outer side ends in the radial direction of the outer peripheral parts with each other; wherein when the outer peripheral parts disposed on both sides of the joint are referred to as first outer peripheral parts, an outer side face in the radial direction of the first outer peripheral part is formed with a recessed part which is recessed toward an inner side in the radial direction; wherein the recessed part is formed between the salient pole part connected with the first outer peripheral part and the joint in the circumferential direction; an outer side face in the radial direction at least of the outer peripheral part except the first outer peripheral part is formed with a second recessed part which is recessed toward an inner side in the radial direction, and wherein the second recessed part is formed at a center position in the circumferential direction of the outer peripheral part as an engaging part which is capable of being pressed toward the inner side in the radial direction; the stator being characterized in that the recessed part is structured of two flat faces (24n, 24p) and a curved face which smoothly connects the flat face with the flat face. a coil; an insulation member; and a stator core provided with a plurality of salient pole parts around each of which the coil is wound through the insulation member; wherein the stator core is provided with an outer peripheral ring part formed in a ring shape and the plurality of the salient pole parts which are protruded from the outer peripheral ring part toward an inner side in a radial direction of the stator and are disposed at a constant interval in a circumferential direction of the stator; wherein the outer peripheral ring part is structured of outer peripheral parts having the same number as that of the plurality of the salient pole parts; wherein the outer peripheral parts are arranged in the circumferential direction and a center in the circumferential direction of each of the outer peripheral parts is connected with the salient pole part; wherein a joint is formed at one position of boundaries in the circumferential direction of the outer peripheral parts; wherein remaining positions of the boundaries in the circumferential direction of the outer peripheral parts except the joint are formed with connecting parts which connect outer side ends in the radial direction of the outer peripheral parts with each other; wherein when the outer peripheral parts disposed on both sides of the joint are referred to as first outer peripheral parts, an outer side face in the radial direction of the first outer peripheral part is formed with a recessed part which is recessed toward an inner side in the radial direction; wherein the recessed part is formed between the salient pole part connected with the first outer peripheral part and the joint in the circumferential direction; an outer side face in the radial direction at least of the outer peripheral part except the first outer peripheral part is formed with a second recessed part which is recessed toward an inner side in the radial direction, and wherein the second recessed part is formed at a center position in the circumferential direction of the outer peripheral part as an engaging part which is capable of being pressed toward the inner side in the radial direction; the stator being characterized in that the recessed part is structured of two flat faces (24n, 24p) and a curved face which smoothly connects the flat face with the flat face.