a differential amplifier circuit unit; and

a replica amplifier circuit unit, wherein:

the differential amplifier circuit unit includes:

first and second transistors provided between a current source circuit and a load circuit, and configured to receive differential input signals at gates thereof to generate differential output signals at drains thereof; and

a third transistor connected between sources of the first and second transistors, and configured to receive a control signal at a gate thereof; and

the replica amplifier circuit unit includes:

a voltage generation circuit configured to generate first and second reference voltages;

first and second replica transistors being replicas of the first and second transistors, the first and second replica transistors being configured to receive the first and second reference voltages at gates thereof to generate replica output signals at drains thereof;

a third replica transistor connected between sources of the first and second replica transistors, and configured to receive the control signal, at a gate thereof; and

an operational amplifier configured to generate the control signal in accordance with a difference between at least one of the first and second reference voltages and the replica output signal, wherein

the operational amplifier is configured to generate the control signal so that a gain of the replica amplifier circuit unit is constant.