Provided is a low stiffness flexible circuit board at a low cost without the sacrifice of conduction reliability between the circuit wiring patterns on the opposite sides of the flexible circuit board. In the double-sided flexible circuit board where copper foils 3 are provided on the opposite sides of a flexible insulating substrate 1 through an adhesive layer 2 and an interlayer conduction passage 4 is formed between circuit wiring patterns formed on the copper foils, the circuit board is formed by bonding a copper foil 7 onto a flexible insulating film 5 having a thickness of <=25 [mu]m anda thermal expansion coefficient in the range of 5-27 ppm/[deg.]C through an adhesive layer 6 having a thickness of 0.3-9 [mu]m, and the interlayer conduction passage is a copper plating layer 8 having a thickness of <=9 [mu]m formed by panel plating.