A wireless device includes an imaging unit having an optical axis which is identical to a radio wave direction of a directional antenna, a reference image is stored in a storage unit, a wireless communication device serving as a communication counterpart and an area around the wireless communication device are photographed at regular intervals, and a control unit compares images photographed at regular intervals with a reference image, calculates a degree of similarity through normalized cross-correlation which is hardly influenced by a change in brightness, calculates an index value indicating a state of a region serving as a monitoring target based on a degree of weighted similarity, detects an abnormality when the index value is a specific numerical value or less, and outputs alert information including the photographed image when a state in which the abnormality is detected is continued for a certain period of time.