A low cost and high speed AF sensor is realized by increasing AF speed without providing a sensor dedicated for a large de-focusing AF. The AF sensor has two sensors each including a plurality of photoelectric conversion elements and detects a focus based on signals read from the sensors. The two sensors each includes a plurality of linear sensors 11 to 13. The two sensors each has a plurality of accumulation controlling circuits (PB detection circuits 14 to 16 and accumulation decision circuits 17 to 19) for controlling the accumulation time of the photoelectric conversion elements and a plurality of scanning circuits (shift registers 21 to 23) for reading out output signals from the photoelectric conversion elements. The AF sensor has a first mode in which the accumulation time of each linear sensor in the two sensors is independently controlled to independently read a signal output and a second mode in which the accumulation time of the linear sensors in the two sensors is collectively controlled to read a signal output.