To form a relief picture on the whole surface of an applied photosensitive resin by directly using a digital image signal in a liquid photosensitive resin plate-making system for flexography.

By repeating a process for forming the relief image to each line by irradiating the photosensitive resin with active beams optically modulated based on the digital image signal while moving a digital exposing device having a plurality of optical switch cells linearly on the photosensitive resin layer applied on a supporting body with a fixed thickness.