A capaciatance detector is provided, which outputs an electric signal dependent on the capacitance present on an object to be measured. The capaciatance detector includes a measurement terminal to be disposed in contact with or in proximity to the object being measured; an impedance conversion circuit connected to the measurement terminal to form a resonant circuit; a reference phase oscillator for supplying a reference phase signal at a constant frequency to the resonant circuit; phase comparison means for outputting, as a capacitance detected signal, a phase difference signal indicative of the phase difference between a resonant signal, which is extracted from the resonant circuit in response to the reference phase signal being applied to the resonant circuit, and the reference phase signal; and resonance frequency regulation means for regulating the resonance frequency of the resonant circuit based on the phase difference signal.