A monitoring apparatus of the present application includes: a transmission antenna section that transmits a radio wave of single beam having a wide angle or alternatively a radio wave having a narrower (angular) range in a plurality of beam directions. A receiving antenna section receives the radio wave transmitted by the transmission antenna section and then reflected by a target. A beam switching instrument performs a switching operation such that power is fed to either a first power feed section or a second power feed section, which thereby controls the beam directions of the radio waves to monitor a specified area.
