A capacitive passenger detector includes: a capacitive sensor having main, sub and guard electrodes; a sensor characteristic measurement unit for applying an alternating voltage signal to each electrode and for converting a current in each electrode to a voltage; and a controller. The controller defines a current in the guard electrode as a reference current when voltages of the main and guard electrodes have a same potential. The controller defines a current flowing direction of the guard electrode to be negative when the voltage of the main electrode is higher than the guard electrode. The controller defines the current flowing direction of the guard electrode to be positive when the voltage of the main electrode is lower than the guard electrode. The controller corrects the voltage of the main electrode based on the current of the guard electrode so that a corrected voltage is set to be a passenger determination data.