A waveguide-microstrip line converter, comprising: a waveguide ; a dielectric substrate that is connected to cover one end of the waveguide ; a strip conductor that is disposed on an end of one surface of the dielectric substrate ; a conductor plate that is disposed substantially in a center of the one surface of the dielectric substrate , and connected to the strip conductor ; a ground conductor that is disposed on another surface of the dielectric substrate except for a connection region of the waveguide and the dielectric substrate ; and a plurality of connection conductors that connect a periphery of the conductor plate and the ground conductor except for a portion that connects the strip conductor and the conductor plate , wherein the ground conductor has an opening formed therein in the connection region of the waveguide and the dielectric substrate , wherein the conductor plate is disposed to cover the opening through intermediation of the dielectric substrate , and wherein the strip conductor and the ground conductor form a microstrip line, characterized in that the plurality of connection conductors is arranged in two lines, each with a segment in the vicinity of the connection portion and a segment in the vicinity of the opening in a longitudinal direction of the microstrip line, wherein said two lines are disposed on opposing sides of the conductor plate so that a distance (D1) between the two lines in the segment in the vicinity of the connection portion of the strip conductor and the conductor plate is narrower than a distance (D2) between the two lines in the segment in the vicinity of the opening . a waveguide ; a dielectric substrate that is connected to cover one end of the waveguide ; a strip conductor that is disposed on an end of one surface of the dielectric substrate ; a conductor plate that is disposed substantially in a center of the one surface of the dielectric substrate , and connected to the strip conductor ; a ground conductor that is disposed on another surface of the dielectric substrate except for a connection region of the waveguide and the dielectric substrate ; and a plurality of connection conductors that connect a periphery of the conductor plate and the ground conductor except for a portion that connects the strip conductor and the conductor plate , wherein the ground conductor has an opening formed therein in the connection region of the waveguide and the dielectric substrate , wherein the conductor plate is disposed to cover the opening through intermediation of the dielectric substrate , and wherein the strip conductor and the ground conductor form a microstrip line, characterized in that the plurality of connection conductors is arranged in two lines, each with a segment in the vicinity of the connection portion and a segment in the vicinity of the opening in a longitudinal direction of the microstrip line, wherein said two lines are disposed on opposing sides of the conductor plate so that a distance (D1) between the two lines in the segment in the vicinity of the connection portion of the strip conductor and the conductor plate is narrower than a distance (D2) between the two lines in the segment in the vicinity of the opening . <EOS>