PURPOSE: To provide a slot feeding plane antenna for linearly polarized wave by which loss is low by a plane structure, a linearly polarized wave is radiated, and that of a plane of polarization of an arbitrary angle being horizontal, vertical, etc., can be assembled and manufactured easily or the plane of polarization can be adjusted.

CONSTITUTION: This antenna is provided with a conductor frame plate 20 provided with a circular inside space, a slot plate 40 which is arranged in front of the abovementioned conductor frame plate 20 so as to form a radial waveguide between a pair of opposed plane conductors and in which plural orthogonal slot pairs are formed by a spiral array as an electromagnetic coupling feeding element to a meander line, circular meander line plates 60, 80 which are arranged through a spacer in front of the slot plate 40 in the circular inside space and in which plural meander lines are formed linearly in parallel, and a cover 100 for covering the front of the circular meander line plates 60, 80, and constituted so that the circular meander line plates 60, 80 can be assembled and manufactured by such a rotation angle as becomes a prescribed plane of polarization or can be adjusted at a prescribed angle.