Devices, methods, and programs control a seat drive mechanism that drives side support parts of a seat. The devices, methods, and programs detect a first curve ahead of a vehicle and a second curve located ahead of the first curve with respect to a travel direction. The devices, methods, and programs predict a between-curves time required to travel between the first curve and the second curve and determine whether the between-curves time is less than a predetermined time, the predetermined time being no less than a time necessary for the side support parts to operate. The devices, methods, and programs control the seat drive mechanism to arrange the side support parts at an action position to support a body of an occupant for the first curve. If the between-curves time is less than the predetermined time, the devices, methods, and programs maintain the side support parts at the action position while traveling the second curve.