PURPOSE: To heighten detection accuracy for an unbalanced position by providing a groove at the end face of a rotary shaft in a motor driven blower which cools a commutator motor by passing a discharge air from the hole part of an end bracket through a housing.

CONSTITUTION: This motor driven blower 1 is constituted of a motor part 2 and a blower part 3, and the motor part 2 is a commutator type motor, and houses a rotor 4 and a stator 5 in the housing 6 and an end bracket 7. The rotor 4 is provided with a rotary shaft 15, and is formed by screw-fixing 16 a radial impeller 9 at a shaft terminal part extending to the blower part 3 side of the rotary shaft 15. Also, a easing 10 is press-fed to the outer periphery of the end bracket 7 by covering the radial impeller 9, which is fixed by holding a fixed guide impeller 8. In such a case, a groove 22 for unbalanced position detection is provided at the end face of the rotary shaft 15, and a signal that becomes a reference is sampled from reflected light from a photodiode, and the unbalance correction position of the rotor 4 can be found.