The present invention relates to a display device that has a plurality of optical sensors provided in a display panel and that can be operated by touching a screen with a finger or pen. A liquid crystal panel with built-in sensors (11) includes a plurality of pixel circuits (1) and a plurality of optical sensors (2) which are arranged two-dimensionally. An MPU (18) selects either a mode that detects a shadow image of an object or a mode that detects a reflection image of the object, based on an illumination of outside light. One frame time is divided into a display period and a sensing period. A backlight (14) is controlled to be turned on during the display period in the shadow image mode and during the sensing period in the reflection image mode, and to be turned off during the sensing period in the shadow image mode and during the display period in the reflection image mode. According to the present invention, the detection accuracy for a touch position is increased while the power consumption of the backlight is suppressed.