An object of the invention is to provide a slot array antenna in which unstable factors for contact of an adjustment portion comprising a slot waveguide and a waveguide holder are removed, a number of parts is decreased to save weight, and assembly is simplified. Accordingly, this invention is to constitute a radiation portion (1) unitedly formed of a slot waveguide (1a), a flare holder (1b), and a supporting portion (1d), if necessary, further adding a screen holder (1c) for a screen (4) for cross polarization suppression. Furthermore, this invention is to constitute a reinforcement feeder (2) unitedly formed of a feeder waveguide (2a), a reinforcement portion (2b) and a reinforcement connector (2c) in the case of an open type antenna.