A capacitance sensor circuit is provided, including: a capacitance variable capacitor changing from a first capacitance to a second capacitance corresponding to environmental change; a reference capacitor; and an amplifier circuit charging the capacitance variable capacitor via a first node and the reference capacitor via a second node, and outputting a determination signal. In the amplifier circuit, a differential amplification part generates a potential difference signal obtained by amplifying the potential difference between the first and the second nodes; an output part outputs the determination signal based on the potential difference signal; and when the difference between the increase degrees of the potentials of the first and the second nodes is less than a predetermined value, the output part holds and outputs the determination signal immediately before that state and a bias control part stops a current flowing through the differential amplification part.