A system includes: a plurality of pixels arranged in a matrix; a reference signal generating unit for generating a ramp signal; A/D converters each arranged correspondingly to each of columns to A/D-convert a signal from the pixel; a counter that performs a count operation according to an output of the ramp signal, and supplies the count signal through the count signal line to the A/D converter; and a counter test circuit that is provided independently from the A/D converter, and tests the counter, based on a matching of the expected value of the count signal with the count signal supplied through the count signal line from the counter. This configuration allows the count signal to be checked concurrently with imaging of an object.