A first ramp signal having a potential which is changed with time in a first amplitude range in a first period and a second ramp signal in which a potential is changed with time in a second amplitude range which includes the first amplitude range and which has maximum amplitude larger than maximum amplitude of the first amplitude range and an amount of the change of the potential per unit time is the same as an amount of the change of the potential per unit time of the first ramp signal are generated, and comparison between an optical signal and the first ramp signal and comparison between the optical signal and the second ramp signal are performed in parallel.