An optical sensor includes a light receiving unit and a calculating unit. The light receiving unit includes a plurality of light receiving elements and a plurality of color filters. The plurality of light receiving elements include a first light receiving element and a second light receiving element through which a photocurrent flows when receiving light. The plurality of color filters include a yellow filter that covers a light receiving surface of the first light receiving element and a red filter that covers a light receiving surface of the second light receiving element. The calculating unit calculates an intensity of a yellow wavelength band based on a difference between a first output signal obtained from the photocurrent of the first light receiving element and a second output signal obtained from the photocurrent of the second light receiving element.