PURPOSE: To increase the utilization rate of the heat energy of a light source device and to perform excellent thermal plate making or thermal copying operation even when an original has a large solid image by pressing alternately a light transmission plate and a pressure plate by using a hydraulic driving device.

CONSTITUTION: A movable exposure table 1 has the light transmission plate 3, light source 4 like a xenon discharge tube, and reflecting mirror 5, and the pressure plate 6 consists of a substrate 7 and a cushion member 8. Working oil is fed to the cylinder chamber 19 of a hydraulic cylinder piston device 16 by the hydraulic pump 15 of the driving device 10 and a piston 18 is elevated to press the original sheet and thermal original paper or thermal copy paper arranged between the light transmission plate 3 and pressure plate 6. When the pressing force attains to a specific constant value, the thermal plate making of the thermal original paper or thermal copying of the thermal copy paper is carried out with heat energy generated by the discharging of the light source device 4. Cosequently, the specific pressing force is maintained for a specific time and the heat energy of the light source device 4 is utilized effectively at a high utilization rate.