A part of bent end sections of a slot is configured to overlap with a waveguide inner wall when seen from the normal direction of a narrow wall surface of a waveguide at which the slot is provided. Thus, the conductance of a single slot can be reduced by adjusting the joined amount of a tip section of the slot and the inner wall of the waveguide. As a result, even in the case where the number of slots provided per waveguide is increased while a waveguide width is restricted to be short with respect to a slot length, impedance matching with a waveguide bonding section can be taken.