PURPOSE: To obtain a stable light quantity distribution without a change in irradiating light quantity against a floated original by compensating the aberration caused by a rod lens collecting the light of an LED array through the scattering of a light with the frost processing.

CONSTITUTION: An LED array 1b is formed by arranging LED chips 11 at a small pitch linearly on a board 13 and lighted by applying a DC voltage to the array 1b. Since the light from the LEDs 11 is diffused as it is and collected by a rod lens 12b. Then the lens 12b is made of a borosilicate glass and frost processing of frosted glass is applied to the entire face to prevent uneven luminous quantity due to aberration and the lens is supported to the optimum position to collect the light by a support 14. Thus, the irradiating light quantity is unchanged even to a floated original and stable light quantity distribution is obtained.