A balanced transmission cable connector includes a balanced transmission cable including a plurality of pair electric wires, each of the pair electric wires including a first signal wire, a second signal wire, and a drain wire; a contact assembly body having an insulative block body where first and second signal contacts and a ground contact are alternately arranged in a row direction, the first and second signal contacts facing each other in a line direction, the block body having a rear surface side where first and second signal wire connecting parts being parts of the first and second signal contacts and a drain wire connecting part and a plate-shaped part being a part of the ground contact project; a first groove part where the first signal wire connecting part is provided; a second groove part where the second signal wire connecting part is provided; a slit and an insulative spacer.