A navigation device (100) estimates a time when a user utilizing the navigation device (100) comes home, and transmits the estimated expected arrival time to a control device (203) in association with the user identifier of the user. In response to receiving the expected arrival times from a plurality of the navigation devices (100), the control device (203) transmits, to an air conditioner (201), a reservation instruction for setting the room temperature at the home to a predetermined target temperature by the estimated arrival time of the earliest user who is supposed to come home earliest. The air conditioner (201) is turned on in accordance with the transmitted reservation instruction among the users.