Disclosed is a process of preparing a planographic printing plate from a light sensitive planographic printing plate material comprising a hydrophilic support and provided thereon, an image formation layer containing (a) an alkali soluble resin with an acid value of 5 to 200 having an acryloyl group or a methacryloyl group, the alkali soluble resin being obtained by reacting a vinyl copolymer having a monomer unit derived from acrylic acid or methacrylic acid with an epoxy compound having an acryloyl group or a methacryloyl group in the molecule, and (b) a diazo resin, the process comprising the steps of imagewise exposing the light sensitive planographic printing plate material to ultraviolet light using an exposure device comprising a digital mirror device (DMD), and removing an image formation layer at non-exposed portions with an aqueous alkali solution to form an image.