1. A process for producing a lithographic printing plate by an ink-jet system comprising: placing a lithographic printing plate precursor comprising a water-resistive support having provided thereon an image receiving layer between a head comprising an emission slit having an emission electrode therein and a counter electrode, and emitting an oily ink from the emission slit by applying voltage according to a digital signal of image pattern information to the emission electrode to form an image on the image receiving layer of the lithographic printing plate precursor; wherein said water-resistive support is a paper support both sides of which are covered with a resin; wherein the resin which covers both sides of the paper support is polyethylene which is a mixture comprising 10 to 90% by weight of a low-density polyethylene having a density of 0.915 to 0.930 g/cc and a melt index of 1.0 to 30.0 g/10 cc and 10 to 90% by weight of a high-density polyethylene having a density of 0.940 to 0.970 g/cc and a melt index of 1.0 to 30.0 g/10 cc; and wherein the oily ink comprises a nonaqueous solvent of an electric resistance of 10.sup.9 .OMEGA.cm or more and a dielectric constant of 3.5 or less and resin particles dispersed therein which are solid at ordinary temperature and are hydrophobic.