An occupant determination apparatus and an occupant determination method accurately determine a size of an occupant, with a simple configuration where a plurality of electrodes are arranged on one layer, and eliminate errors due to the capacitance between an occupant and surrounding car-body metal parts or the like, and thus suppress erroneous determination. The apparatus includes a sensor having a plurality of seat section electrodes arranged on a sitting section, and a determination section. The determination section includes an oscillator, a capacitance detecting section which detects the current flowing through a seat section electrode in order to detect the capacitance, a switching circuit which switches the connection of the capacitance detecting section to the seat section electrode, and a controlling section which outputs a switch control signal.