To attain the improvement of charge conversion efficiency and lowering of dark current.

In an optical mixing system provided with a photosensitive layer, at least two modulation gates and at least two reading electrodes are connected to the photosensitive layer, and the potential of the modulation gate are mutually connected between both the gates. The modulation gate is connected to a modulation device fluctuating to the reading electrode corresponding to a desired modulation function, preferably, constant potential. In order to attain the improvement of the charge conversion efficiency and the lowering of the dark current by further developing the known optical mixing system, each reading electrode has at least two separation electrode parts arranged at a constant interval.