Provided is a 4-transistor CMOS image in which a driving condition or a pixel structure is changed so that a transfer transistor in a pixel operates in a pinch-off condition during reset and transfer operations in order to reduce dark current and fixed-pattern noise caused by a change in an operation condition of the transfer transistor and inter-pixel characteristic discrepancy. The image sensor includes a photosensitive pixel including a transfer transistor for transferring photon-induced charges created in a photodiode; and a voltage control unit for controlling a turn-on voltage applied to a gate of the transfer transistor to be lower than a floating diffusion node voltage plus the threshold voltage of the transfer transistor during a partial or entire section of a turn-on section of the transfer transistor such that the transfer transistor operates in a pseudo pinch-off mode.