To sufficiently strengthen the directivity of an antenna.

An antenna device 110 is formed by wiring a linear conductor spirally with a first space P using a prescribed axis S as a center and comprises a helical antenna 111 for radiating a radio wave with circular polarization toward the axis S. In addition, the antenna device 110 comprises a wave director 112 placed along the direction of the axis S toward which the helical antenna 111 radiates a radio wave with a second space X substantially the same as the first space P from the helical antenna 111.