PURPOSE: To eliminate the adverse influence of outside harmful light and to maintain a tube wall at optimum temperature by providing a light intensity detecting means detecting the intensity of light from a fluorescent lamp and supplying or stopping electric power to the lamp according as increase in detected intensity light or its decrease.

CONSTITUTION: The original lighting fluorescent lamp 2 of an original lighting device is provided with a lighting control means LC, and the light intensity detecting means PD provided between a main body control part 20 provided on the means LC and the lamp 2 controls electric power supplied to the lamp 2. The power supply to the lamp 2 continues while the number of detecting signals increases according to the light intensity detected by an optical sensor 28, a photoelectric transfer circuit 29 and a microcomputer 26, when the control part 20 stands by, not in copying actions. The power supply to the lamp 2 stops in a prescribed time after the number of the detecting signals start decreasing. A fluorescent lamp control part 25 controls the power supply to the lamp 2 so that the tube wall of the lamp 2 is maintained at temperature providing a maximum light emitting efficiency.