An occupied seat detection device includes: at least one receiver that is disposed in a space including a plurality of seats and receives at least one of sound generated inside the space or sound generated outside the space; an acoustic characteristics analyzer that calculates, from a signal received by the at least one receiver, temporal characteristics or frequency characteristics of the sound in the space; and a detector that detects whether an occupant is present or whether an occupied seat is present inside the space, based on the temporal characteristics or the frequency characteristics calculated by the acoustic characteristics analyzer, and outputs a detection result.