A seat occupancy determination device configured to be provided at one of seating portions of a plural vehicle seats includes a pair of seat occupancy amount detection devices detecting a seat occupancy amount increasing and decreasing in response to a change of a load applied to each portion of the seating portion, a seat occupancy state determination device determining a seat occupancy state of the vehicle seat, an unbalanced load detection device detecting a degree of unbalance of the load applied to a right portion and a left portion of the seating portion, and a seat occupancy threshold value setting device setting a seat occupancy threshold value and correcting the seat occupancy threshold value in response to the degree of unbalance of the load applied to the right portion and the left portion of the seating portion based on a detected signal transmitted from the unbalanced load detection device.