A rotation detector includes a motor, a current detector and a hardware processor. The motor includes coils of two or more phases and a rotor. The current detector detects currents flowing in coils of at least two phases among the coils of two or more phases. The hardware processor estimates an initial position of the rotor based on current values of the currents detected by the current detector to start the motor, controls an energization pattern on the phases to rotate and start the motor based on the estimated initial position, and determines whether the rotor stops or is rotating before completing the estimation of the initial position.