An object of the present invention is to provide a flexible printed wiring board which relaxes stress concentration in the flexible printed wiring board during production steps, thereby preventing wire breakage in inner lead portions and cracking in solder resist which would otherwise be caused during mounting of devices such as IC chips and LSI chips. The flexible printed wiring board of the present invention includes an insulating layer; a wiring pattern formed of a plurality of wirings being juxtaposed, which wiring pattern is formed through patterning a conductor layer stacked on at least one surface of the insulating layer and on which wiring pattern a semiconductor chip is to be mounted; and grid-like dummy patterns formed in a blank area where the wiring pattern is not provided, wherein the dummy patterns are formed in a width direction generally symmetrically with respect to the longitudinal direction of the flexible printed wiring board.