PURPOSE: To provide a wireless security device which improves the noise resistance.

CONSTITUTION: A wireless security device includes an addition averaging means 15 which calculates an addition average equivalent to several cycles for each cycle for the signals that can be extracted from the sections where the answer signals should be included, a frequency analyzing means which divides the output signal of the means 15 into plural frequency bands, neural network 9 which is connected to the frequency analyzing means through an input layer of the network and previously learnt so as to output through an output layer the affirmative value when the signals including an answer signal are supplied through the input layer and to output the negative value when only the noises are supplied through the input layer respectively, and a deciding means 10 which decides the presence or absence of an answer signal by the output value of the network 9. In such a constitution, a state monitoring part 1 decides the presence or absence of the answer signal received from a sensor part 2.