An electric motor comprising: a ring-shaped stator that includes a field coil; and a rotor that holds a permanent magnet in a magnet holding portion on an outer circumference thereof in an exposed state and is supported to be rotatable about a rotary shaft core in an inner space of the stator, wherein the magnet holding portion has a magnet insertion portion (Sa) which is more depressed in a rotary shaft core direction than an outer circumference of a rotor yoke configuring the rotor, the magnet holding portion has an opening portion, which is formed in an outer circumferential position of the rotor yoke in the magnet insertion portion (Sa), the magnet holding portion has a pair of regulation bodies which are integrally formed with the rotor yoke in a form of extending toward a central side of the opening portion in a circumferential opening width direction of the opening portion, and the permanent magnet is configured to include a cylindrical outer wall surface whose radius is equivalent to that of the outer circumference of the rotor yoke, a flat rear wall surface which is a side opposite to the outer wall surface, a pair of side wall surfaces which are both end portions of the permanent magnet defining a magnet width of the permanent magnet in a circumferential direction of the rotor yoke, and a pair of engaged surfaces which are formed by partially notching the outer wall surface so as to cause the regulation bodies to fit and abut thereon at both end positions on the outer wall surface in the circumferential direction, characterized in that in the magnet insertion portion (Sa), a groove-shaped portion (Sg) having a width in the circumferential direction wider than the magnet width of the permanent magnet in the circumferential direction is formed so as to allow a bottom surface of the permanent magnet to fit, and expansion portions (Se), which expand, on the outer circumference side of the groove-shaped portion (Sg), on both circumference ends of the groove-shaped portion (Sg) further than the groove-shaped portion (Sg) in a circumferential direction, are formed such that an extending length of the regulation bodies in the circumferential direction is expanded by forming the expansion portions (Se), and the permanent magnet is held by utilizing an elastic deformation of the regulation bodies. a ring-shaped stator that includes a field coil; and a rotor that holds a permanent magnet in a magnet holding portion on an outer circumference thereof in an exposed state and is supported to be rotatable about a rotary shaft core in an inner space of the stator, wherein the magnet holding portion has a magnet insertion portion (Sa) which is more depressed in a rotary shaft core direction than an outer circumference of a rotor yoke configuring the rotor, the magnet holding portion has an opening portion, which is formed in an outer circumferential position of the rotor yoke in the magnet insertion portion (Sa), the magnet holding portion has a pair of regulation bodies which are integrally formed with the rotor yoke in a form of extending toward a central side of the opening portion in a circumferential opening width direction of the opening portion, and the permanent magnet is configured to include a cylindrical outer wall surface whose radius is equivalent to that of the outer circumference of the rotor yoke, a flat rear wall surface which is a side opposite to the outer wall surface, a pair of side wall surfaces which are both end portions of the permanent magnet defining a magnet width of the permanent magnet in a circumferential direction of the rotor yoke, and a pair of engaged surfaces which are formed by partially notching the outer wall surface so as to cause the regulation bodies to fit and abut thereon at both end positions on the outer wall surface in the circumferential direction, characterized in that in the magnet insertion portion (Sa), a groove-shaped portion (Sg) having a width in the circumferential direction wider than the magnet width of the permanent magnet in the circumferential direction is formed so as to allow a bottom surface of the permanent magnet to fit, and expansion portions (Se), which expand, on the outer circumference side of the groove-shaped portion (Sg), on both circumference ends of the groove-shaped portion (Sg) further than the groove-shaped portion (Sg) in a circumferential direction, are formed such that an extending length of the regulation bodies in the circumferential direction is expanded by forming the expansion portions (Se), and the permanent magnet is held by utilizing an elastic deformation of the regulation bodies.