PURPOSE: To reduce uneven density by keeping recording density uniformly by increasing the light emitting strength of a laser beam for image data with low picture element density, and decreasing it for the image data with high picture element density.

CONSTITUTION: A density setting part 24 sets the light emitting strength of a laser diode LD based on density designated by a control panel 22 and the dot density of dot data outputted from a data conversion part 23. For example, when the dot data in an area with low picture element density is transferred from the data conversion part 23, it is converted into the dot data to which the light emitting strength is designated to the density designated by the control panel 22. Also, when the dot data in an area with high picture element density is transferred from the data conversion part 23, the dot data is converted into the one to which the light emitting strength less by dot density exceeding the density designated by the control panel 22 is designated.