A physical quantity detection system includes a pixel array unit including pixels two-dimensionally arranged in a matrix, where each of the pixel converts an externally supplied physical quantity into an electrical signal, a readout unit configured to read out a signal from each of the pixels n times by changing the sensitivity each time, where n is an integer greater than or equal to 2, a storage unit configured to store m signals out of the n signals read out from the pixel, where m is an integer greater than or equal to 1 and is less than n, and a write control unit configured to compare the signal read out from the pixel by the readout unit with a predetermined threshold value and configured to control a write operation of the signal into the storage unit on the basis of the comparison result.