An image sensor comprising a number of light sensor circuits each representing a unit pixel and capable of outputting a sensor signal corresponding to a photo current produced in a photoelectric converting element in proportion to light falling thereon, which is provided with a way of detecting a period and a phase of flicker in light from a light source and a way of determining timing of obtaining the maximum brightness of the light source based on the flicker detection signal and reading sensor signals from respective pixels at the timing determined. This image sensor can easily prevent the effect of flicker resulting from flicker of the light source to an image taken and displayed by the image sensor with no need for adjusting the time of accumulating a charge in the capacitor in accord with incident light thereon and compensating an image signal to be displayed.