SEATING STATE DETECTION DEVICE

A seating state detection device includes an acquisition unit configured to acquire a detection signal group in a predetermined period that is output as a result of transmission and reception of waves by a radio wave sensor mounted on a vehicle, a signal extraction unit configured to extract specific-intensity signals in a predetermined reflection intensity range from the detection signal group, and a determination unit configured to determine whether an occupant in the vehicle is in a first riding state in which the occupant is directly seated on a seat or in a second riding state in which the occupant is seated in an infant auxiliary device, based on a distribution mode of the specific-intensity signals.