In Japan, there are frequent incidents of injuries caused by common bladed objects (knives, kitchen knives, etc.). To prevent such incidents, it is effective to install gate-type metal detectors in facilities, stores, public transportation, etc. that are used by an unspecified number of people, to detect the carrying of bladed objects. They can also be used to prevent the bringing in of smartphones and the leakage of information due to the removal of USB memory sticks.