To provide an inexpensive small-sized antenna for a radio unit with a thin profile that is used for diversity reception.

In the small-sized antenna for a radio unit that is used for the radio unit and consists of a shield case 2 and a printed circuit board 1 contained in the shield case 2, an antenna element 4 consisting of a metallic foil pattern of a meandering shape is formed on the printed circuit board 1. One end 5 of the antenna element 4 connected to an internal reception circuit is used for a feeding point, the other end of the antenna element 4 is open to form a 1st monopole antenna element, the shield case 2 and a planar ground layer formed in the printed circuit board 1 form a shield box 7, which forms a 2nd monopole antenna element, and the 1st monopole antenna element and the 2nd monopole antenna element form a dipole antenna.