A circuit substrate capable of reducing and preventing deviations of circuit characteristics includes a relatively hard region and a relatively soft region. A main body of the circuit substrate includes a stack of a plurality of flexible sheets made of a flexible material and includes rigid regions and a flexible region, the flexible region being more easily deformable than the rigid regions. Wiring conductors are disposed in the main body and define circuitry. Reinforcing insulative films are disposed so as to cover the portions where the wiring conductors are not disposed in the rigid regions on the flexible sheets when seen in plan view from the z-axis direction.