PURPOSE: To reduce the size and to enhance the performance of a motor by regulating a gap between a resolver rotor and a resolver stator due to an eccentricity of a rotational shaft for the motor by the rotation of a spacer.

CONSTITUTION: Motor 1 has a rotor shaft 2 which includes a small-diameter shaft portion 2a extending integrally from the end of the shaft 2. A resolver 6 attached to the motor 1 has a hollow cylindrical resolver rotor shaft 20, and a resolver rotor 9 is provided on the outer periphery of the shaft 20. Further, a resolver stator 8 is secured to the inner periphery of a cylindrical frame 21. The rotor 9 is attached at its shaft 20 by a retainer 22 to the shaft 2a, and the stator 8 is attached at its mounting flange 21a through a spacer 23 to the outside of an end cover 5. In this case, the spacer 23 is formed in a hollow annular unit having a crank-like cross section, faucet faces 23a, 23b engaged closely with one another are formed, and the centers are eccentrically displaced. Thus, an unbalance of a gap between the stator 8 and the rotor 9 is corrected.