PURPOSE: To obtain an image exposing device which is small in size and low in cost by providing an emission intensity switch means for varying emission intensity in a dot unit of a light emitting section at every emission so as to reduce the number of parts of an exposure head.

CONSTITUTION: An image data of 8 bits is divided into eight within 1 dot unit in a vertical scanning direction Y. For example, when a gradation level 1 is to be expressed, a first bit in the 8-bit image data is selected by a selector circuit 8 as a means for varying the number of emissions. At this time at the selector circuit 8, a voltage V1 is selected corresponding to the first bit, inputted to an amplifier 6 in a constant current source 4 through an addition circuit 7, an electric current (i) flows to an LED 2, so that the LED 2 emits light in accordance with the value of the current (i). When a gradation level 24 is to be expressed, V8 and V16 of the selector circuit 8 are selected and a lighting signal is turned on only when the current is 8i and 16i. When a gradation level 25 is to be expressed, V1-V128 are selected and the lighting signal is turned on at all times of currents i-128i.