An object of the present invention is to provide an electronic circuit device capable of reducing the occurrence of electromagnetic waves associated with the propagation of a signal by utilizing light as a signal. The electronic circuit device has a transparent substrate (hereinafter written as a substrate) over which an optical sensor and an optical shutter and an electronic circuit composed of thin film transistors (TFTs) are formed. An optical signal is inputted from an external into the electronic circuit device, the optical signal is directly irradiated on the optical sensor over the substrate, and penetrates through the substrate, and inputted into an optical sensor over another substrate. The optical sensor converts the optical signal into an electronic signal, and the circuit over the substrate operates. A control signal controls the optical shutter, a light is inputted from the external into this optical shutter, and whether it is transmitted or it is interrupted is determined, whereby the signal is taken out.