(Technical Problem) To provide a lightweight and highly reliable plug connector for high-speed digital multi-channel transmission. (Technical Solution) A rigid substrate of a plug connector includes a base material having a first surface, including a first side and a second side formed opposite the first side, and a second surface formed opposite the first surface, and a plurality of signal transmission patterns configured to transmit a differential signal, and includes a first signal transmission pattern on the first surface, a second signal transmission pattern on the second surface, a third signal transmission pattern on the first surface and adjacent to the first signal transmission pattern, and a fourth signal transmission pattern on the second surface and adjacent to the second signal transmission pattern. Each signal transmission pattern includes a first conductor pattern, a second conductor pattern forming a differential pair, and a third conductor pattern having a fixed potential. Each of the first conductor pattern, the second conductor pattern, and the third conductor pattern includes a terminal portion electrically connected to a terminal of another connector, a pad portion electrically connected to a cable, and a wiring portion electrically connecting the terminal portion and the pad portion. The terminal portion is formed along the first side, and the pad portion is formed along the second side.