A display device with a touch pad function is provided which reduces the elements required to form a photo sensor while still accurately detecting input coordinate positions. The display device includes a display part on which a plurality of pixels are arranged in a matrix array, a plurality of photo detection circuits which are arranged in a matrix array in the inside of the display part, wherein each photo detection circuit of the plurality of photo detection circuits includes: a photo sensor which converts an incident light into a optical current corresponding to intensity of the incident light, an integral capacitance which integrates the optical current converted by the photo sensor, and a comparator to which a voltage of the integral capacitance is inputted, and the comparator includes a transistor of an open drain output type with a grounded source.