To improve a gain of an antenna. An antenna 1 includes a dielectric layer 6, a conductive ground layer 7 bonded to the layer 6 and including active slots 7c-7f aligned at regular intervals, aligned active elements 9c-9f formed facing the active slots 7c-7f, respectively, first passive elements 9b, 9a aligned with and extending from one end of a row of the active elements 9c-9f, second passive elements 9g, 9h aligned with and extending from the other end of the row, a feed line 4a formed on a side opposite to the layer 7 with respect to the layer 6, to be electromagnetically coupled to the active elements 9c-9f via the active slots 7c-7f. The second passive elements 9g, 9h are arranged in line symmetry with the first passive elements 9b, 9a with respect to a line 9z passing through the center of the row and perpendicular to the row.