A passenger determination device includes a load sensor attached to a seat main body, a controller for calculating a detected load value on the basis of an outputted load value of the load sensor and for determining a passenger on the basis of a large and small relationship between the detected load value and a predetermined determination threshold value, a load variations detecting device for detecting variations of the detected load value when the large and small relationship between the detected load value and a predetermined determination threshold value changes and a prohibition device for prohibiting from changing the determination of the passenger by the change of the large and small relationship between the detected load value and a predetermined determination threshold value when the detected load variations is small.