An analog-to-digital converter has a first digital signal generator that generates a first digital signal based on whether or not a sampling signal of an input signal is equal to or lower than a signal corresponding to a second reference signal higher than a first reference signal, a first slope generator to generate a first slope signal that changes with time from the sampled and held signal equal to or lower than the first reference signal, a second slope generator to generate a second slope signal that changes with time from the sampled and held signal to a signal level equal to or lower than the second reference signal, and a second digital signal generator that generates a second digital signal based on a time at which the first slope signal matches the first reference signal or a time at which the second slope signal matches the second reference signal.