A focusing apparatus includes an image pickup element that includes a plurality of unit cells including a first pixel and a second pixel corresponding to a same microlens, a detector configured to detect a phase difference of an image signal of a first pixel group and an image signal of a second pixel group that correspond to a focus detection region, a focus controller configured to perform a focus control based on a detection result of the detector, an exposure controller configured to control an exposure value based on an output from the image pickup element, the detector detects the phase difference of an image signal generated by sequentially switching a plurality of focus detection regions, and the exposure controller controls the exposure value so as to be fixed until the detector completes a detection of the phase difference in the plurality of focus detection regions.