To provide an electric circuit structure with which the occurrence of sound generation caused by vibration of a circuit element mounted on a flexible substrate connected to a circuit board is suppressed. The electric circuit structure includes a mechanical member (9) in the form of a frame having a closed bottom; a circuit board (1) on the surface of which an electric circuit element is formed, the circuit board being accommodated in the mechanical member (9); a flexible substrate (10) that has a connecting terminal formed on one end (10a) thereof, the connecting terminal being connected to an electrode terminal (7) formed on the circuit board (1), and that is folded back and fixed to a rear face of the mechanical member (9) at the other end opposite to the one end (10a); and a circuit element mounted on a portion of the flexible substrate (10) that is folded back to the rear face of the mechanical member (9), wherein the flexible substrate (10) is fixed to the rear face of the mechanical member (9) via a nonwoven fabric adhesive tape employing a nonwoven fabric as a base material.