A plurality of house [a], the empty chamber by a common key, in the key management for managing real estate thereof, reducing the burden of handling the empty room can be efficiently managing system. A plurality of house [solution] 11a - 11e, 12a - 12e by a real estate management system 10 in a room, a plurality of housing 11a - 11e, 12a - 12e of the, main lock the empty chamber 31d, 31e, 32d, 32e of the key 50 is common. Figure 1 [drawing]