An image sensor includes an imaging area including a plurality of cells arrayed in a matrix on a semiconductor substrate, each of the cells including an avalanche photodiode, the avalanche photodiode including: an anode region buried in an upper portion of the semiconductor substrate; a cathode region buried in the upper portion of the semiconductor substrate separated from the anode region in a direction parallel to the surface of the semiconductor substrate; and an avalanche multiplication region defined between the anode and cathode regions, the avalanche multiplication region having an impurity concentration less than the anode and cathode regions; wherein depths of the anode and cathode regions from the surface of the semiconductor substrate are different from each other.