In a power detector, a comparator for detection receives an input signal and a reference voltage, and compares the input signal to the reference voltage around the switching time of active and inactive states of the output of the comparator in accordance with an output of an input switching signal generator. Except for the switching time, an input voltage for non-use of the comparator is inputs to the comparator for detection, and the differential inputs are fixed to the same potential. Therefore, aging reduction in the accuracy of power detection caused by BT degradation is effectively mitigated.