An occupant sensing method includes steps of: sensing installation of a child seat on a seat of a vehicle; storing a detection value of a load sensor which is provided to be attached to the seat and detects an input load as a first load value, when the installation of the child seat is sensed; storing a detection value of the load sensor as a second load value when a predetermined time period has elapsed from a time point at which the installation of the child seat is sensed; and estimating a load change amount at the time of getting on/off which is a change amount of a load that is generated as the occupant gets on/off the child seat, based on a difference value between the first load value and the second load value.