PURPOSE: To make ridge lines in the main scanning direction and oblique direction of a picture flat with a simple means scarcely increasing the number of LEDs per unit length, by arranging alternately a wide light emitting element and a narrow light emitting element.

CONSTITUTION: An interval of light emitting sections is used as an interval d1 the same as the conventional method, the width of LEDs B, D is used as W2, the width W3 of LEDs A, C, E is increased more than the width W2 and the LEDs B, D and the LEDs A, C, E are arranged alternately, in the arrangement of the shape and size of LED section exposing and scanning a light irradiated from the LEDs of a light emitting element (LED) array chip 1 on a line 3 on the photo sensitive body via a focusing rod lens array. Then, the diameter of light image by the LEDs A, C, E is increased and the ridge lines in the main scanning direction and oblique direction of the picture are improved in comparison with the conventional method.