Image sensor and image-capturing apparatus

An image sensor comprising:

• a plurality of substrates that are laminated on each other, wherein:
• the plurality of substrates includes:
• a first pixel that includes (i) a first photoelectric conversion unit that photoelectrically converts light to an electric charge, (ii) a first transfer unit that transfers the electric charge converted by the first photoelectric conversion unit to a first floating diffusion, and (iii) a first transistor that includes a gate electrically connected to the first floating diffusion and outputs a first signal that is based on the electric charge transferred to the first floating diffusion, and
• a first conversion unit that converts the first signal output from the first pixel into a digital signal, the first conversion unit including (a) a first comparator circuit includes a first input terminal to which the first signal is input, (b) a first group of latch circuits configured to store a plurality of bits, and (c) a second group of latch circuits con figured to store a plurality of bits, the first group of latch circuits and the second group of latch circuits being storage circuits that store a first digital signal converted from the first signal to the digital signal wherein
• the second group of latch circuits is arranged, among the plurality of substrates, on a different substrate from a substrate on which the first group of latch circuits is arranged.