An image sensor including a pixel that includes: a first photodiode; a second photodiode having a larger light-receiving area than the first photodiode; a first floating diffusion node accumulating charges of the first photodiode; a second floating diffusion node accumulating charges of the second photodiode; a capacitor accumulating charges overflowing from the first photodiode; a first switch transistor having a first end connected to the first floating diffusion node and a second end connected to the capacitor; and a driving transistor configured to convert the accumulated charges into a pixel signal, the first switch transistor is turned on in a low conversion gain (LCG) mode of a readout section of the first photodiode, and is turned off in a high conversion gain (HCG) mode of the readout section of the first photodiode, and the readout circuit generates image data based on pixel signals from the first and second sections.