To easily and surely make initial registration of an accurate magnetic force level corresponding to an actual installed situation in the installation field.

Initial registration operation comprises operating a crescent lock opening/closing lever into an unlocked position to open a cover member in the kept-away state of a magnet and to operate a registration switch 60, and operating the opening/closing lever into a locked position in the closed state of the cover member within one minute to bring the magnet closer. A registration processing section 74 is operated by the operation of the registration switch 60 to make initial registration of the magnetic force level Vs detected by a locking detecting Hall sensor 48, into a nonvolatile memory 68 and to set locking and unlocking determination thresholds TH based on the registered magnetic force level Vs. A power source stabilizing timing setting section 74 discriminates the stop timing of a circuit operation for fluctuating power source voltage supplied from a battery 44, and acquires the magnetic force level detected by the locking detecting Hall sensor 48.

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