To improve reliability and to easily secure the resonance space of a built-in alarm part by making a gate side alarm part output an alarm by a resonance circuit at the time of being passed through a separately installed gate in the state of being kept attached to merchandise.

When a cord body is cut, the cord body is moved to the side of a switch 15 by a coil spring along with an acting body and the acting body is abutted to the switch 15 and operates it. Then, a buzzer driving circuit 21 functions and operates a buzzer structure part 19 and reporting sound is outputted. Also, when this self-ringing type burglar-proof tag passes between gate constitution parts, by the action of the resonance circuit 13 inside the self-ringing type burglar-proof tag, specified frequency components are absorbed from radio waves outputted from a gate constitution part side and modulated. Thus, since the radio waves received by a reception part on the gate constitution part side are turned to the ones from which the specified frequency components are removed, they are detected in a modulation signal detection part 61, display is performed at a display part 63 and prescribed reporting sound is outputted by a reporting sound output part 65.