1. An image pickup apparatus comprising: an image sensor that includes a plurality of first pixels and a plurality of second pixels; a focus state detector that detects a focus state according to a pair image based on pixel signals from the plurality of second pixels; and a controller configured to control output of signal from the image sensor, wherein the controller controls the output in a frame such that, in mixing and output signal mode, the signals from a group of the plurality of first pixels are mixed and are output by a scanning circuit, the signals from the plurality of second pixels are not mixed and are output by the scanning circuit, and image based on the signal from the image sensor is displayed in the frame.