The intruder detection device for deciding the occurrence of an invasion if an electric wave, which is received by a leakage transfer passage on the receiving side juxtaposed to a leakage transfer passage on the transmitting side for receiving a leakage electric wave from the transmitting leakage transfer passage, changes, and the intruder detection device comprises: a plurality of reference spectrum diffusion signal generating means; a plurality of correlating means configured together with the reference spectrum diffusion signal generating means on a common sensor card, for collating the output reference spectrum diffusion signal of the reference spectrum diffusion signal generating means with the received signal from the receiving leakage transfer passage; and setting means for adjusting the detection precision which is determined by the reference spectrum diffusion signal generating means and the correlating means.