To provide a rotation angle detector integrated with a motor and for detecting a rotational angle without fail.

A first capacitor 41 is connected parallel to a first pole winding 21 of a rotor 20, provided to a stator for relative rotation. A second capacitor 42, whose electrostatic capacitance is less than the first capacitor 41 is connected, in parallel with a second pole winding 22. An AC power source 53 is superimposed on a DC power source 50, which energizes a winding of the rotor 20 through a commutator 30. Since the impedance of a circuit formed between brushes 51 and 52 varies among three states due to the rotation of the rotor 20, a current-detecting means 54 detects currents of three amplitude states. A signal-detecting part 55 and a rotational angle detecting part 56 detect the rotating direction of the rotor 20 from the order of state transition of current amplitude, and by increasing/decreasing a counted value of state transition frequency according to the rotational direction the rotational angle of the rotor or of an object which is driven is calculated.