An image display unit and a method of detecting an object which are capable of reliably detecting an object with a simple structure irrespective of use conditions are provided. Invisible light is emitted from a screen of a display portion. The invisible light reflected from a target object which comes in contact with or close to the screen is received on the screen. On the basis of the received invisible light, the target object is detected. Thus, the target object can be reliably detected without influence of the display state of the display portion, and influence of use conditions such as surrounding circumstances (the case where it is bright or dark). Moreover, for example, it is not necessary to separately arrange a component such as a touch panel, so the image display unit can be achieved with a simple structure.