An inner-rotor-type motor, comprising: a stator including a stator core and a coil, the stator core including a ring-shaped core-back portion and a plurality of main poles protruding radially inward from the core-back portion, the coil wound around each of the main poles through an insulator (16, 18); a rotor rotatably arranged inside the stator so as to face tip ends of the main poles and provided with a rotor shaft extending along a center axis; and cover members (30, 32) arranged so as to cover axial opposite sides of the stator and configured to hold bearings (34, 36) which support the rotor shaft, wherein the core-back portion of the stator core has a substantially square shape, the core-back portion including side surfaces corresponding to four sides of a square, the side surfaces of the core-back portion configured to form motor outer surfaces; the insulator (16, 18) includes two insulating members (16, 18) mounted to the stator core at the axial opposite sides thereof, each of the insulating members (16, 18) including a plurality of slot insulating portions (16a, 18a) which covers the main poles and an octagonal frame portion (16b', 18b') which interconnects the slot insulating portions (16a, 18a) at an axial end surface side of the stator core, the frame portion (16b', 18b') including four outer surface portions (16d, 18d) substantially flush with the motor outer surfaces of four sides of the core-back portion; each of the cover members (30, 32) includes an end plate portion (30a, 32a) configured to form an end surface of the motor and provided with a bearing holding portion (30b, 32b) in a central region thereof, and four leg portions (30c, 32c) arranged in four corners of the end plate portion (30a, 32a) and configured to make contact with axial end surfaces of four corner portions of the stator core; each of the outer surface portions (16d, 18d) of the frame portion (16b', 18b') of each of the insulating members (16, 18) inserted between the leg portions (30c, 32c) of each of the cover members (30, 32); and the frame portion (16b', 18b') of each of the insulating members (16, 18) includes a base-side ring-shaped frame (16b1, 18b1) having a smaller diameter, a tip-end-side ring-shaped frame (16b2, 18b2) having a larger diameter, and a ring-shaped thin portion (16b3) which interconnects the base-side ring-shaped frame (16b1, 18b1) and the tip-end-side ring-shaped frame (16b2, 18b2). a stator including a stator core and a coil, the stator core including a ring-shaped core-back portion and a plurality of main poles protruding radially inward from the core-back portion, the coil wound around each of the main poles through an insulator (16, 18); a rotor rotatably arranged inside the stator so as to face tip ends of the main poles and provided with a rotor shaft extending along a center axis; and cover members (30, 32) arranged so as to cover axial opposite sides of the stator and configured to hold bearings (34, 36) which support the rotor shaft, wherein the core-back portion of the stator core has a substantially square shape, the core-back portion including side surfaces corresponding to four sides of a square, the side surfaces of the core-back portion configured to form motor outer surfaces; the insulator (16, 18) includes two insulating members (16, 18) mounted to the stator core at the axial opposite sides thereof, each of the insulating members (16, 18) including a plurality of slot insulating portions (16a, 18a) which covers the main poles and an octagonal frame portion (16b', 18b') which interconnects the slot insulating portions (16a, 18a) at an axial end surface side of the stator core, the frame portion (16b', 18b') including four outer surface portions (16d, 18d) substantially flush with the motor outer surfaces of four sides of the core-back portion; each of the cover members (30, 32) includes an end plate portion (30a, 32a) configured to form an end surface of the motor and provided with a bearing holding portion (30b, 32b) in a central region thereof, and four leg portions (30c, 32c) arranged in four corners of the end plate portion (30a, 32a) and configured to make contact with axial end surfaces of four corner portions of the stator core; each of the outer surface portions (16d, 18d) of the frame portion (16b', 18b') of each of the insulating members (16, 18) inserted between the leg portions (30c, 32c) of each of the cover members (30, 32); and the frame portion (16b', 18b') of each of the insulating members (16, 18) includes a base-side ring-shaped frame (16b1, 18b1) having a smaller diameter, a tip-end-side ring-shaped frame (16b2, 18b2) having a larger diameter, and a ring-shaped thin portion (16b3) which interconnects the base-side ring-shaped frame (16b1, 18b1) and the tip-end-side ring-shaped frame (16b2, 18b2).