PROBLEM TO BE SOLVED : To provide a lock device and a real-estate management system using the same, which allow a real estate company to manage a lock of a vacant room without making a person in charge go to an actual place and which enable a lighthearted inspection of the many rooms to be carried out by a person desiring the inspection. SOLUTION : This lock device locks an entrance door by fixing one side to the entrance door and latching the other side on a room side, and unlocks the entrance door according to a radio signal from without. The lock device has a reception part for the radio signal, a signal recognition part which recognizes the received signal so as to provide an unlocking instruction, an operation part which makes the lock operate in accordance with the unlocking instruction, and a power supply part for them. The lock device, which has a mounting part freely attached to/detached from the entrance door, is mounted on the arbitrary door in order to operate unlocking of the door by remote control and manage the vacant room.