An intrusion detection device includes a plurality of intrusion detection sensors (1) each configured to detect intrusion of an object into a security area W and output a warning signal; and a bracket (2) having a single device-mounting surface (2c) and a plurality of sensor-mounting surfaces (2d) on which the respective intrusion detection sensors (1) are mounted such that predetermined angles thereof different from each other are maintained. The bracket (2) includes a hollow portion (S) in which a wire between each intrusion detection sensor (1) is installed. In addition, each intrusion detection sensor (1) includes an optical section (3) including: a main unit (3A) which includes a detection element (30); and a unit holder (4) which rotatably supports the main unit (3A), and the security area (W) is adjusted such that a direction thereof is changed, by rotation of the main unit (3A).