To provide a test coupon for finely adjusting a value of differential impedance in a configuration that width and an interval of signal lines are fixed.

In a test coupon 100, a pattern on a principal surface and a pattern on the rear surface form signal lines and ground patterns, respectively, and are integrated. A part of the ground pattern on the rear surface is a mesh part 111, and is a mesh-like pattern. Thus, in comparison with a configuration that the whole rear surface is the ground pattern, an impedance value becomes high for about dozens of ohms. A residual copper rate is varied stepwise to display the residual copper rate by an indicator on the principal surface of the test coupon 100. By the above configuration, the residual copper rate by TDR measurement is contrasted with a change point of the differential impedance to be visually confirmed.