An amplifier circuit unit is composed of an offset compensation circuit for equalizing and issuing a DC potential in data input period of one input signal of differential input signals, and a DC potential in data input period of other input signal, and an amplitude limiting amplifier circuit for receiving a differential output signal from this offset compensation circuit as an input signal, and issuing to a differential output terminal as a differential output signal kept in a constant output signal amplitude while amplifying in a linear region. This amplifier circuit unit is connected in cascade in plural stages as required, and is applied to an amplifier circuit of an optical receiving circuit and others.