An occupant determination device for a vehicle seat includes a load sensor provided at a seat body, a controller for calculating a detection load value based on a load value output from the load sensor and for determining an occupant sitting on the vehicle seat by comparing the detection load value and a predetermined threshold value, a determining means for determining whether or not a child restraint system is equipped on the vehicle seat based on a variation of the detection load value and a detecting means for detecting whether or not the vehicle is stopped. When a vehicle stop condition is not detected by the detecting means, the determining means does not determine whether or not the child restraint system is equipped on the seat.