PURPOSE: To improve the precision of operation by installing a space modulation element which light beams can spatially and freely rewrite transmissivity and permitting a light-emitting element array to irradiate the space modulation element with rewriting light beams.

CONSTITUTION: A light-receiving element array 3 receives and detects an incident irradiating light from the light-emitting element array 1. A threshold processing is executed by permitting a threshold processing circuit 4 to electrically threshold-process the detection result of the array 3 and to feedback- control the array 1. The circuit 4 feedback controls the light-emitting element array 1, spatially varies the transmissivity of the space modulation element 5 and displays a learning function. Consequently, a calculation error which is due to the variance of the light-emitting element array and which cannot be corrected in a mask whose transmissivity is fixed is eliminated and the precision of operation improves. Since the space modulation element has the effect of a light guiding refractive index and whose transmissivity can spatially and freely be rewritten by the light beams, and the pattern is directly written in a material, there is no problem in a resolution and the calculation of a large capacity is attained.