An electric motor including a housing and a circular stator core, the housing having an inner circumferential surface, the housing also having a first predetermined thermal expansion coefficient, the housing further having an elastic part, the circular stator core being pressed to an inside of the housing by tight fit, the stator core having an outer circumferential surface, the stator core also having a second predetermined thermal expansion coefficient that is different from the first predetermined thermal expansion coefficient, a void is defined between the inner circumferential surface and the outer circumferential surface so as to prevent the inner and the outer circumferential surfaces (25a, 16c) from contacting each other in a circular region, when the housing and the stator core expand or shrink so as to tightly fit each other due to a differential between the first and the second predetermined thermal expansion coefficients, the elastic part which corresponds to the void being elastically deformed; the housing has a cylindrical circumferential wall; and three or more contacting portions are provided, where the stator core is supported by the circumferential wall; characterized in that: the stator core comprises protrusions between first recesses, and the circumferential wall of the housing comprises second recesses, wherein each contacting portion includes a distal end surface of the protrusion, wherein a first void element is provided between the circumferential wall and the stator core by forming the second recess in the inner circumferential surface of the circumferential wall of the housing, the second recess being formed by outwardly expanding a part of the elastic part of the circumferential wall, which corresponds to the second recess, in the radial direction of the stator core, wherein a second void element is provided between the circumferential wall and the stator core by forming the first recess in the outer circumferential surface of the stator core, wherein the void includes the first void element and the second void element, and wherein in a waved-shape of the circumferential wall in the circumferential direction of the stator core, which waved-shape is formed by the outward expansion of each the elastic parts, a vertex of each waved-shape is arranged at intervals of an unequal angle around a central axis of the stator core. a void is defined between the inner circumferential surface and the outer circumferential surface so as to prevent the inner and the outer circumferential surfaces (25a, 16c) from contacting each other in a circular region, when the housing and the stator core expand or shrink so as to tightly fit each other due to a differential between the first and the second predetermined thermal expansion coefficients, the elastic part which corresponds to the void being elastically deformed; the housing has a cylindrical circumferential wall; and three or more contacting portions are provided, where the stator core is supported by the circumferential wall; the stator core comprises protrusions between first recesses, and the circumferential wall of the housing comprises second recesses, wherein each contacting portion includes a distal end surface of the protrusion, wherein a first void element is provided between the circumferential wall and the stator core by forming the second recess in the inner circumferential surface of the circumferential wall of the housing, the second recess being formed by outwardly expanding a part of the elastic part of the circumferential wall, which corresponds to the second recess, in the radial direction of the stator core, wherein a second void element is provided between the circumferential wall and the stator core by forming the first recess in the outer circumferential surface of the stator core, wherein the void includes the first void element and the second void element, and wherein in a waved-shape of the circumferential wall in the circumferential direction of the stator core, which waved-shape is formed by the outward expansion of each the elastic parts, a vertex of each waved-shape is arranged at intervals of an unequal angle around a central axis of the stator core.