A solid-state image sensor comprises unit pixels, each unit pixel including photodiodes, transfer switches, a floating diffusion portion, and reset means, and an AD converter, wherein the AD converter includes a reference signal generator and a comparator that compares the reference signal and analog signal and vary an output depending on a magnitude relationship, the floating diffusion portion accumulates a first signal obtained by transferring a signal of at least one of the photodiodes, and adds, to the first signal, a second signal obtained by transferring a signal of at least one of the photodiodes, and the AD converter operates in a first AD conversion mode when AD-converting the first signal, and operates in a second AD conversion mode when AD-converting the second signal.