A slot array antenna includes: a first conductive member having a first conductive surface and a plurality of slots therein, the slots being arrayed in a first direction and in a second direction which intersects the first direction; a second conductive member having a second conductive surface which opposes the first conductive surface; a plurality of waveguide members arrayed between the first and second conductive members along a direction which intersects the first direction, each waveguide member having an conductive waveguide face which extends along the first direction so as to oppose at least one of the slots; and an artificial magnetic conductor in a subregion which is within a region between the first and second conductive members but outside of a subregion containing the waveguide members. Neither an electric wall nor an artificial magnetic conductor exists in a space between two adjacent waveguide faces among the waveguide members.