PROBLEM TO BE SOLVED: To detect abnormality in a frequency of a sine wave applied to an capacitance sensor.SOLUTION: The capacitive occupant detector includes a sensor characteristics measurement part 14 applying a sine wave SC to a capacitance sensor 31 disposed in a seat of a vehicle and converting a current from the capacitance sensor 31 to a voltage value, a CPU 15 determining a detecting object on the seat from the voltage value, a reference capacitor 52 connected to a route applying the sine wave SC from the sensor characteristics measurement part 14 to the capacitance sensor 31 to apply the sine wave SC in place of the capacitance sensor 31, and ROM or EPROM 16 of the CPU 15 where a logical voltage equivalent to a voltage obtained by the sensor characteristics measurement part 14 is stored as a reference voltage V1 when a sine wave SC of a predetermined frequency is applied to the reference capacitor 52. The CPU 15 determines the frequency of the sine wave SC abnormal if the voltage obtained by the sensor characteristics measurement part 14 is not equivalent to the reference voltage V1 when the sine wave SC is applied to the reference capacitor 52 in place of the capacitance sensor 31.