An image sensor includes a photoelectric conversion unit configured to receive light to generate an electric charge and provide the electric charge to a first node, a transfer transistor configured to provide a voltage level of the first node to a floating diffusion node in response to a first signal, a booster configured to increase a voltage level of the floating diffusion node in response to a second signal, a source follower transistor configured to provide the voltage level of the floating diffusion node to a second node, and a selection transistor configured to provide a voltage level of the second node to a pixel output terminal in response to a third signal. After the selection transistor is turned on, the booster is enabled, and before the transfer transistor is turned on, the booster is disabled.