PURPOSE: To copy all original with intermediate density to similar copy density automatically with appropriate contrast, by bringing the light emission quantity of an illumination light source under nonlinear control to the output integral value of an original density detecting means.

CONSTITUTION: The relation between original density and the amount of light emission is nonlinear, and the amount of light emission is increased for a high- density original or decreased for a low-density original so that nearly equal copy density is obtained within an intermediate density range. The specific nonlinear characteristic curve of the relation between the original density and the amount of light emission is stored in an ROM5, and a CPU4 refers to it to control the amount of light emission. The output integral value of a photodetecting means 1a or detection 1 for a surface potential 1b is inputted to an A/D converter 2, input port 3, and the CPU4. Density data is compared with the address of said characteristic curve in the ROM5 to decide data on the amount of light emission and the amount of light emission of the light source 12 is adjusted through an D/A converter 6 according to the data on the amount of light emission by controlling an applied voltage.