Provided is a waveguide-microstrip line converter, including: a waveguide; a dielectric substrate that is connected to cover one end of the waveguide; a strip conductor that is disposed on a front surface of the dielectric substrate; a conductor plate that is disposed the front surface of the dielectric substrate, and connected to the strip conductor; a ground conductor that is disposed on a rear surface of the dielectric substrate; and a plurality of connection conductors that connect a periphery of the conductor plate and the ground conductor, in which: the ground conductor has an opening formed therein in a connection region; the strip conductor and the ground conductor forma microstrip line; and the plurality of connection conductors are arranged so that a distance between two lines of the plurality of connection conductors that are aligned in a longitudinal direction of the microstrip line, and disposed on both opposing sides of the conductor plate in a vicinity of a connection portion is narrower than a distance therebetween in a vicinity of the opening.