A sheet discriminating device, wherein, when a starting element (6) is switched on, a self-holding circuit (5) is switched to a conduction state from a non-conduction state to allow a battery (1) to supply power to a drive control device (2), a discrimination sensor (4) and a conveying device (3) via the self-holding circuit (5). When not in use, the self-holding circuit (5) is switched to a non-conduction state to restrict a battery (1) power consumption, thereby extending a battery (1) replacing timing or a charging cycle and significantly prolonging a battery life.