To provide an offset printing device, with a plate making process function on a printer, which realizes a computer-to-press arrangement omitting an entire intermediate process such as film output and printing of a printing plate.

This offset printing device comprises a plate cylinder 3 with a forward pawl 1 and a rear pawl 2 which chuck the printing plate S wound around a peripheral face, a soaking device 4, an inking device 5, a rubber cylinder 6 and an impression cylinder 7. In addition, a heat transfer printer P for making the printing plate S is of such a construction that the ink ribbon of an ink ribbon cassette 12 is brought into close contact with a manuscript paper So having water retention characteristics and a heat-sensitive head 18 is heated to sublimate and transfer the oil ink of the ink ribbon to the manuscript paper So and that thus the printing plate S is made by drawing a picture in image lines. Further, a feed direction regulating guide 13 which conducts the tip edge of the printing plate S made by the heat transfer printer P to a position where the tip edge is chucked by the forward pawl 1, a rear edge presser 16 which presses the rear edge of the painting plate S to a position where the rear edge is chucked by the rear pawl 2 and a printing plate recovery device 17 which recovers the printing plate S to be separated from the plate cylinder 3 by disengaging the chucking action of the forward pawl 1 and the rear pawl 2, are provided.