A producing method of a wired circuit board that can prevent meandering of the elongate base material conveyed with the rolls and also prevent entry of air bubbles in between a light-transparency protecting film and a photosensitive solder resist layer when the light-transparency protecting film is laminated on the photosensitive solder resist layer. After a conductive pattern 3 is formed on the front side of the elongate base material 1 by the additive process, a narrow stiffener sheet 7 smaller in width than the elongate base material 1 is provided on the back side of the elongate base material 1. Then, after the photosensitive solder resist layer 10 is formed on the front side of the elongate base material 1 to cover the conductive pattern 3, the light-transparency protecting film 11 is laminated on the front side of the photosensitive solder resist layer 10. Thereafter, the photosensitive solder resist layer 10 is exposed to light through the light-transparency protecting film 11. Then, after the light-transparency protecting film 11 is stripped off from the photosensitive solder resist layer 10, the photosensitive solder resist layer 10 was developed and then cured by heating. Thereafter, the narrow stiffener sheet 7 is stripped off from the elongate base material. The flexible wired circuit board is produced in the manner described above.