A first constant voltage circuit includes an operational amplifier having a reference voltage applied to a first input terminal thereof and a voltage obtained as a result of an output voltage being divided applied to a second input terminal thereof, and controls an output transistor with an output of its operational amplifier. A second constant voltage circuit includes an operational amplifier having a reference voltage applied to a first input terminal thereof and a voltage obtained as a result of the output voltage being divided applied to a second input terminal thereof, and controls the output transistor with an output of its operational amplifier, a current consumption of the second constant voltage circuit being smaller than a current consumption of the first constant voltage circuit. A switching part is provided for each of those operational amplifiers and makes connection and disconnection between an output terminal of the operational amplifier and the output transistor. A switching logic circuit controls the switching units so that the first constant voltage circuit is connected to the output transistor when the load is in the operation condition but the second constant voltage circuit is connected to the output transistor when the load is in the standby condition.