To provide a compact direction detection antenna of directional switching type that is easy to install.

A conductor plate contacted with an antenna element at an angle of 90 degrees is disposed, and a plurality of antenna elements for obtaining directivity are configured to be similar to a ground type vertical antenna. This allows the omission of one of dipole type elements, thereby achieving an easy-to-install compact structure. A signal to control a switching element for switching the directivity is sent from a receiver to a feeder line. Wiring for a control signal is omitted by turning on/off the switching element correspondingly to the signal. A connection between the receiver and a direction detection antenna can be configured only by the single feeder line.