To provide an actuator for a valve having a lower possibility of failures by holding energization of an excitation brake for a set time in a case of an instantaneous power failure and preventing a power spring from being unwound and wound to elongate life.

In the actuator for an emergency-open/close type valve wherein the power spring is wound to hold a pressure accumulated state by the excitation brake simultaneously when the valve is closed or opened by driving a motor and the valve is closed or opened by a restoration force of the power spring by a shut-off of power, an electric double-layered capacitor is provided in a motor drive circuit, a locked state of the excitation brake holding the pressure accumulated state of the spring is prevented from being unlocked due to the instantaneous power failure by discharge of the capacitor.