To eliminate the deviations of the horizontally and vertically polarized wave directions of radio waves and to uniformize radiation of both polarized wave components by setting the antenna area ratio of a horizontal loop antenna part to a vertical loop antenna part to be within a specific range.

In a transmission circuit 1, a stripline-shaped horizontal loop antenna part 4 is formed along a main surface of a circuit board 2 and a U-shaped vertical loop antenna part 6 is formed by erecting from the main surface respectively. And, the part 4 is constituted of the base end part 4a of the U shape and an extending part 4b extending from its one end, and a coil part 8 for inductance adjustment is connected to the front end of the part 4b. In such a case, the ratio (=SH/SV) of the antenna area SV of the part 6 to the antenna area SH of the part 4 is set so as to be between 2.0 and 6.5.