PURPOSE: To attain plural types of conversion and to secure an application suited to the processing of various large-scale optical data with low cost, by showing the intensity of the light made incident to a photocell in the form of a function of the total intensity of the light made incident to an optical system as well as in the form of a function of the voltage impressed to each modulation element.

CONSTITUTION: A modulation signal 12 is applied to a selected store position address of a charge store register 2 by a store position selector 1. Thus the electric charge is stored, and the variation of the prescribed voltage in the electric charge is stored into a store register 12. Then the electric charge of each cell is supplied to a photocell of a photodetector 5 via an optical modulation element 4. The optical characteristics of the element of a modulator 3 are shown in the form of a function of the total intensity of the light made incident to the corresponding optical system for the intensity of the light made incident to the photocell and at the same time controlled by the electric charge of a cell related to the register 2 so as to obtain a function of the voltage applied to each modulation element 4. Then the electric charge produced at the photocell of the detector 5 is transferred to a CCD shift register 8 by a separatable photoelectric charge transfer gate 6 and then integrated.