A solid-state image pickup apparatus which is capable of enlarging dynamic range and taking images at high frame rate. The solid-state image pickup apparatus has a pixel unit having first pixels with a first sensitivity to the light and second pixels with a second sensitivity lower than the first sensitivity, and the first pixels and the second pixels being alternately arranged in a row direction. Pixel signals are read out from the first pixels as first pixel signals, and analog-to-digital conversion of the first pixel signals is performed to obtain first digital signals. Pixel signals are read out from the second pixels as second pixel signals, and analog-to-digital conversion of the second pixel signals is performed to obtain second digital signals. The first digital signals and the second digital signals are output as image data.