PURPOSE: To make the subject devices inexpensive to produce and compact in size by providing a control mean which maintains the output of solid laser always at such a level as not to allow a sensitized paper to be exposed and, at the time of printing, increases the output of a semiconductor laser or add thereto the output of a separate semiconductor laser.

CONSTITUTION: When a sensitized paper is printed by a green colored laser, the excitation light produced by a semiconductor laser 14 enters Nd: YAG rod 20. When the output of the excitation light is not less than the threshold value, the excited rod 20 generates a fundamental wave, this wave passes through KTP22 in an optical resonator 12 to be converted into a second high-frequency wave and the green colored laser is produced from an output mirror 26 and passes through a light deflecting device 44 to scan over a capsule paper 46. The output of the green colored laser beams 14 depends on that of the excitation light. Therefore, if the out put of the excitation light of the semiconductor laser 14 is small, the output of the green colored laser becomes so small that the capsule paper 46 is not exposed. In this condition, when the excitation light is also produced from the semiconductor laser 32, the excitation light is also produced from the semiconductor laser 32, the excitation light is doubled to produce a sufficient green colored laser to expose the capsule paper 46.