In a rotation detecting apparatus, while a switch is in an on state so that electrical power is supplied from a power source to a controller via the switch, the controller receives, as a first output signal, an output signal output from an output unit of a first rotation sensor, and receives, as a second output signal, an output signal output from an output unit of the second rotation sensor. The first output signal includes at least the first rotational information and the second rotational information based on the first rotation sensor, and the second output signal includes at least the first rotational information and the second rotational information based on the second rotation sensor. The controller determines whether there is a malfunction in each of the first and second rotation sensors as a function of the first output signal and the second output signal.
