An imaging apparatus comprising: a pixel unit having a plurality of pixels, each of the pixels being configured to generate a signal based on an electric charge generated by photoelectric conversion; and a comparator configured to perform a first comparison operation of comparing the signal (Va) based on the electric charge with a comparison signal (VREF), and configured to perform a second comparison operation, wherein the comparator is configured to perform, in a first case that a result of the first comparison operation indicates that an amplitude of the signal (Va) based on the electric charge is less than an amplitude of the comparison signal (VREF), the second comparison operation of comparing the signal (Va) based on the electric charge with a first reference signal having a voltage changing in a first changing ratio with respect to time to a first voltage (VL), and to perform, in a second case that the result of the first comparison operation indicates that the amplitude of the signal (Va) based on the electric charge is greater than the amplitude of the comparison signal (VREF), the second comparison operation of comparing the signal (Va) based on the electric charge with a second reference signal having a voltage changing in a second changing ratio with respect to time, which is greater than the first changing ratio, and wherein an amplitude of the comparison signal (VREF) is less than an amplitude of the first voltage (VL). a pixel unit having a plurality of pixels, each of the pixels being configured to generate a signal based on an electric charge generated by photoelectric conversion; and a comparator configured to perform a first comparison operation of comparing the signal (Va) based on the electric charge with a comparison signal (VREF), and configured to perform a second comparison operation, wherein the comparator is configured to perform, in a first case that a result of the first comparison operation indicates that an amplitude of the signal (Va) based on the electric charge is less than an amplitude of the comparison signal (VREF), the second comparison operation of comparing the signal (Va) based on the electric charge with a first reference signal having a voltage changing in a first changing ratio with respect to time to a first voltage (VL), and to perform, in a second case that the result of the first comparison operation indicates that the amplitude of the signal (Va) based on the electric charge is greater than the amplitude of the comparison signal (VREF), the second comparison operation of comparing the signal (Va) based on the electric charge with a second reference signal having a voltage changing in a second changing ratio with respect to time, which is greater than the first changing ratio, and to perform, in a first case that a result of the first comparison operation indicates that an amplitude of the signal (Va) based on the electric charge is less than an amplitude of the comparison signal (VREF), the second comparison operation of comparing the signal (Va) based on the electric charge with a first reference signal having a voltage changing in a first changing ratio with respect to time to a first voltage (VL), and to perform, in a second case that the result of the first comparison operation indicates that the amplitude of the signal (Va) based on the electric charge is greater than the amplitude of the comparison signal (VREF), the second comparison operation of comparing the signal (Va) based on the electric charge with a second reference signal having a voltage changing in a second changing ratio with respect to time, which is greater than the first changing ratio, and wherein an amplitude of the comparison signal (VREF) is less than an amplitude of the first voltage (VL).