An armature structure for a three-phase motor, comprising: 6N (N is a natural number) slots; 1N coils per phase; 3N main poles; and 3N auxiliary poles, wherein a coil wound around a winding bobbin inserted into the slot is wound around the main pole, the coil is not wound around the auxiliary pole, the main poles and the auxiliary poles are alternately placed, the winding bobbin includes a barrel portion and a flange portion, the barrel portion is in contact with a side surface in a circumferential direction of the main pole in the slot, said side surface extending along a first plane, the flange portion rises in the slot from the barrel portion along a first outer peripheral bottom portion of the slot, said first outer peripheral bottom portion having a surface extending along a second plane, the second plane being perpendicular to the first plane, characterised in that a side surface in the circumferential direction of the auxiliary pole extends along a third plane, a surface of a second outer peripheral bottom portion of the slot extends along a fourth plane, the fourth plane intersecting the third plane, and an outer peripheral surface of the coil extends along a fifth plane, the fifth plane being parallel to the first plane and intersecting the third and fourth planes (B2 and C2), such that a gap area is defined that is not occupied by the coil, in the slot, the gap area having in its cross-section a triangular shape, and the second outer peripheral bottom portion is continuous to the first outer peripheral bottom portion, the surface of the second outer peripheral bottom portion extending along the fourth plane intersecting at an angle the surface of the first outer peripheral bottom portion extending along the second plane. 6N (N is a natural number) slots; 1N coils per phase; 3N main poles; and 3N auxiliary poles, wherein a coil wound around a winding bobbin inserted into the slot is wound around the main pole, the coil is not wound around the auxiliary pole, the main poles and the auxiliary poles are alternately placed, the winding bobbin includes a barrel portion and a flange portion, the barrel portion is in contact with a side surface in a circumferential direction of the main pole in the slot, said side surface extending along a first plane, the flange portion rises in the slot from the barrel portion along a first outer peripheral bottom portion of the slot, said first outer peripheral bottom portion having a surface extending along a second plane, the second plane being perpendicular to the first plane, characterised in that a side surface in the circumferential direction of the auxiliary pole extends along a third plane, a surface of a second outer peripheral bottom portion of the slot extends along a fourth plane, the fourth plane intersecting the third plane, and an outer peripheral surface of the coil extends along a fifth plane, the fifth plane being parallel to the first plane and intersecting the third and fourth planes (B2 and C2), such that a gap area is defined that is not occupied by the coil, in the slot, the gap area having in its cross-section a triangular shape, and the second outer peripheral bottom portion is continuous to the first outer peripheral bottom portion, the surface of the second outer peripheral bottom portion extending along the fourth plane intersecting at an angle the surface of the first outer peripheral bottom portion extending along the second plane.