the invention provides a signal processing apparatus having clamp capacitance device for receiving , at one electrode thereof , first and second signals outputted from a signal source , a signal transfer transistor of which one main electrode is connected to an other electrode of the clamp capacitance device , signal accumulating capacitance device connected to an other main electrode of the signal transfer transistor , and reset device for fixing the potential of the signal accumulating capacitance device , wherein the potential of the signal accumulating capacitance device is fixed by the reset device while the first signal is outputted from the signal source and the signal accumulating capacitance device is maintained in a floating state while the second signal is outputted from the signal source , and the signal transfer transistor is controlled in such a manner that the potential of the main electrode of the signal transfer transistor and that of the other main electrode thereof show different saturation operations while the signal charge is transferred through the clamp capacitance device and the signal transfer transistor during the output of the first and second signals , thereby causing the saturation current to transfer the signal charge .