A medium processing apparatus includes a sensor that is intermittently energized and detects a predetermined physical quantity and outputs the detection value in the energization period, the sensor stabilizing its output after an output stabilization period, which is shorter than the energization period, has lapsed, a storage unit that stores the detection value that has been detected by the sensor before the lapse of the energization period and after the lapse of the output stabilization period, and a controller that reads the detection value from the storage unit and performs a predetermined process by using the detection value read.