A rotation detecting apparatus for detecting a rotational state of a direct-current motor includes a driving device, a control device, an energization detecting device, an alternating-current component detecting device, and a rotational state detecting device. An impedance between brushes of the motor changes periodically in accordance with rotation of the motor. The alternating-current component detecting device detects change of an alternating-current component of electric current that is supplied to the motor based on an electrical quantity. The change of the alternating-current component is caused by change of the impedance caused in accordance with the rotation. The rotational state detecting device detects at least one of a rotation angle, a rotational direction, and a rotational speed of the motor based on a detection result of the alternating-current component detecting device.