PURPOSE: To simplify a structure and reduce a cost to enable secure seating detection by using a thermal diffusion plate as a detection electrode of a seating sensor.

CONSTITUTION: A thermal diffusion plate 2 for diffusing heat generated by a heater wire 1 is used as a detection electrode 4 of a capacitance-type seating sensor. Since this thermal diffusion plate 2 does not lose its function even if it is optionally separated, the thermal diffusion plate 2 is divided into both side parts 2a and front and rear edges 2b for example so that both side parts 2a of the thermal diffusion plate 2 are used as the detection electrodes 4. Since portions where a human body is less likely to touch are not used as the detection electrodes, a rate of capacitance change can be prevented from being small, so that secure detection of the human body is possible.