A contact detector circuit that detects a change in a DC sensor signal based on a change in a physical amount to be detected includes: a reference signal generation circuit that generates a reference signal based on the DC sensor signal; a trigger signal output circuit that compares the DC sensor signal with the reference signal and outputs a trigger signal based on a result of the comparison; and a sampling-and-holding circuit that holds the reference signal when the trigger signal is started to be outputted and outputs the held reference signal to the trigger signal output circuit while the trigger signal is outputted. The trigger signal output circuit uses the reference signal outputted by the sampling-and-holding circuit for the comparison with the DC sensor signal while the trigger signal is outputted.