According to one embodiment, a pixel outputs a photoelectrically converted signal. A reference ramp generating circuit generates a first ramp wave and a second ramp wave having a step width smaller than that of the first ramp wave. A column ADC circuit performs switching between the first ramp wave and the second ramp wave on the basis of the signal level of the signal from the pixel, compares the ramp wave with the signal level, and detects a signal component of the pixel by CDS.