An electrostatic capacitance sensor, includes an electrostatic capacitance detector, an operational amplifier in which a feedback impedance circuit is connected between an output terminal and an inverse input terminal of the operational amplifier, a signal line connected between the inverse input terminal of the operational amplifier and the electrostatic capacitance detector, an alternating-current signal generator connected to a non-inverse input terminal of the operational amplifier, and a shield for shielding at least a portion of the signal line, the shield being connected to the non-inverse input terminal of the operational amplifier and the alternating-current signal generator. The electrostatic capacitance detector includes a detecting electrode and a shield electrode. The detecting electrode includes a detector-detecting electrode for detecting an object to be detected and an electrode introducer-detecting electrode for introducing an electrode to the detector-detecting electrode. The shield electrode is connected to the shield. At least a portion of the electrode introducer-detecting electrode is shielded by the shield electrode.