To provide a focus detector with which the pixel arrangement corresponding to the dense focal position in the imaging area can be performed and the monitoring region of the focal detection processing can be flexibly selected even in the multiple focal detection system.

A camera system according to the present invention has a focal detection mechanism which sets the detection area of pixel output respectively for a plurality of pixel columns in a area sensor position 27, makes the maximum detection circuits C1 to C14 select the pixel output corresponding to the detection range set from the pixel output of the pixel columns of the area sensor position 27 as valid signals, and controls the pixel accumulation of each pixel columns by detecting the output of pixels selected by the maximum detection circuits C1 to C14 as valid signals.