Disclosed are an illuminance sensor which has a spectral-response characteristic approximate to the spectral luminous efficacy and which has a low circuit complexity, and a display device including the illuminance sensor. The illuminance sensor includes (i) a current output circuit which, with use of a bitstream signal of a first analog-digital conversion circuit for carrying out an analog-digital conversion with respect to a first current flowing through a first light receiving element, outputs a current corresponding to the first current and (ii) a second analog-digital conversion circuit which receives a third current obtained by subtracting a current from a second current flowing through a second light receiving element and which thus carries out an analog-digital conversion with respect to the third current.