To provide a theft detector at a low cost by utilizing an existing car detector in a two-stage type parking device.

The two-stage type parking device is constituted in such a manner that a changeover switch SW changing over a circuit 10 for lifting and lowering aiming at the putting-in and taking-out of a car and the theft detector 20 aiming at the theft detection of the car is installed, the circuit 10 is detached by photoelectric switch switching-relay contact C2R2 when the theft detector 20 is selected, electricity is conducted through an alarm device BZ and an alarm is given when a photoelectric switch PH does not detect the car 31, and an electric conduction through the alarm device BZ is interrupted by the photoelectric-switch switching-relay contact C2R1 conducting reverse working when a lowering circuit 10b for the circuit 10 is selected. Since the theft detector can be configured only by partially changing a conventional car detector and adding irreducible parts, the inexpensive theft detector can be provided.