An AD converting unit compares an output signal from an amplifier circuit after reset of a pixel with a reference signal of time-variable, outputs a first digital value, when the output signal from the amplifier circuit in a non-reset state of the pixel is larger than a threshold, sets a gain of the amplifier circuit to a first gain, when the output signal is smaller than the threshold, sets the gain of the amplifier circuit to a second gain larger than the first gain, further after the gain of the amplifier circuit was set to the first or second gain, compares the output signal from the amplifier circuit in the non-reset state of the pixel with the reference signal of time-variable, and outputs a second digital value. When resolutions of the first and second digital values differ, a correcting unit corrects a difference between the resolutions.