1. An image sensor comprising: a pixel unit including an effective pixel region and blanking regions and having a plurality of pixels each outputting a pixel signal, the blanking regions including optical black pixels and dummy pixels; an amplifier amplifying the pixel signals output from the pixel unit; and a defective pixel detection circuit performing a defective pixel detection on signals output from the amplifier, wherein, the defective pixel detection circuit adjusts the detection accuracy of the defective pixel detection in accordance with an exposure condition of the pixel unit.