A series-regulator type of power supply circuit is provided. In the circuit, the emitter and collector of a transistor are connected to power input/output terminals. A control circuit controls a base current of the transistor based on the output voltage detected at the power output terminal and a given target voltage. A resistor circuit connects the base and the collector of the transistor. A bypass circuit connects the emitter and the base of the transistor and passes a bypass current. The accepting circuit connected to the power output terminal accepts (absorbs) current from an output current. An amount of the acceptance current is equal to or larger than an amount of the bypass current and a product of the bypass current and a resistance value of the resistance circuit is equal to or more than a difference between a voltage at the power input terminal and the target voltage.