An image sensor using three-color, e.g., R, G, and B light-emitting elements assures a period in which all the three colors are turned on and periods in each of which one light-emitting element is turned off during a scan period per pixel, and integrates and measures amounts of light of the respective periods. An amount of light based on the OFF light-emitting element is calculated based on a difference between the amounts of light during the full light-ON period and each light-OFF period to define an amount of light of the light-emitting element, and light intensity information corresponding to each light-emitting element is obtained based on a total amount of light during the entire scan period per pixel, and the amount of light of each light-emitting element.