A connector for balanced transmission includes a block member having input and output contact pairs formed on front and back surfaces thereof, and a relay wiring substrate having front and back surfaces with a ground layer in between, on which surfaces input contact connecting pads, output contact connecting pads, input wiring patterns, and output wiring patterns are formed. Each input contact pair includes a pair of contact parts formed on the front or back surface of the block member and a pair of lead parts connected to the input contact connecting pads formed on the front or back surface of the relay wiring substrate. Each output contact pair includes a pair of contact parts formed on the front or back surface of the block member and a pair of lead parts connected to the output contact connecting pads formed on the front or back surface of the relay wiring substrate.