To provide an intrusion detection device that can be easily mounted, has less influence of rain or snow, has a weather resistance, and can cope with various shapes. In the intrusion detection device of the present invention, pressure sensitive means (14) that is a flexible cable-like piezoelectric sensor is stored in a packet (13) in a sealed state, and mounted on a wall-like structure (11) such as a veranda, a balcony or a fence for the domicile. Since the packet is slidable, the pressure sensitive means is sufficiently deformed when the wall-like structure (11) is pressed, so that the sensor can make the detection reliably.