A wheel assembly rotational position identifying apparatus includes an acceleration detector, a control section, and a battery. The control section identifies the rotational position of the wheel assembly based on an acceleration detected by the acceleration detector. The control section operates in a control mode that is a selected one of a normal mode and a power saving mode, in which a power consumption associated with identification of the rotational position of the wheel assembly is smaller than that in the normal mode. The control section switches the control mode to the normal mode when an initiation condition is met in accordance with an input from outside. The control section also switches the control mode to the power saving mode when a termination condition is met in the normal mode.