An image sensor has blocks of light-receiving elements which are switched by respective associated thin-film transistors. Charges generated in the light-receiving elements are transferred to respective common signal lines through a matrix wiring on a block basis. Capacitor forming lines are formed above the common signal lines in a crossed relationship through an interposed insulating layer to provide a capacitance substantially equal to a source-gate overlap capacitance of each thin-film switching transistor. A voltage signal in an inverse phase relation to a gate control signal is applied to the capacitor forming lines to cancel out coupling of the gate control signal to the potential of the common signal lines.