An amplifier circuit includes a potential relation between a common emitter amplifier circuit (amplifier circuit body) including an NPN transistor (bipolar transistor) and a clamp circuit which maintains a potential relation between a base-collector of the NPN transistor of the common emitter amplifier circuit. The clamp circuit includes a level shift circuit and a clamp diode for suppressing a decrease in the collector potential of the NPN transistor of the common emitter amplifier circuit.