An image input apparatus. A detection section detects a change cycle of an intensity of an external light inputted to a camera. A timing control section synchronizes the change cycle of the intensity of the external light with a plurality of input timings of the camera by changing a phase difference in order. An evaluation section compares each storage quantity of the external light inputted to the camera at the plurality of input timings synchronized by the timing control section for each phase difference. A selection section selects the phase difference whose difference of the storage quantities of the external light is smallest from all phase difference changed by the timing control section.