An occupant monitoring device which is provided in a vehicle, and monitors one or more occupants riding in the vehicle. The occupant monitoring device includes: a recognizer that recognizes one or more occupants riding in the vehicle; a monitor that monitors the one or more occupants riding in the vehicle according to a result of recognition of the one or more occupants by the recognizer; a start controller that individually starts or stops the recognizer and the monitor. The start controller starts the recognizer in a stopped state of the monitor.