An optical sensor able to make a pixel area small without degrading an increase of the speed of detection of the change of light intensity and reduction of the power consumption, therefore able reduce the size of a chip at the time of an increase of pixels and a method of selection of pixels of the same, imparting a function of holding charges corresponding to a light reception intensity of a previous frame and a function for comparing strongness/weakness of the light reception intensity of the previous frame and the light reception intensity of the current frame to each of the pixels composing a pixel array part and configuring both function portions by a capacitor Cs connected between a photodiode PD and a selection transistor T2.