A stator structure includes: a stator core (104) having a large number of concave slots (105) and a large number of convex magnetic poles (106) circumferentially alternately arranged; and magnet wires (101) of rectangular cross section in each of which an insulating coating (103) is formed on the outer surface of a metal wire (102), wherein each of the slots (105) is formed so that the distance (W2) between both the side surfaces (109, 109) of the slot (105) gradually decreases from the bottom (107) to a distal opening (108) of the slot (105), each of the magnet wires (101) is wound around the associated magnetic pole (106) and inserted in tiers in the associated slot (105), and the magnet wire (101) is placed in the slot (105) so that the width (W1) thereof continuously or stepwise decreases from the bottom (107) to the distal opening (108) of the slot (105).