To provide an expansive display method of an information device linked with an ordinary input operation image screen even if the expanding function is used, and capable of displaying a required input key and information.

An expansive display selecting means 45 is arranged on the input operation image screen 40. A plurality of preset input keys 42, 43, 44 and 45 are expansively displayed on the basis of operation of this expansive display selecting means 45. L5 is made small from a distance L1 between the respective input keys, and the plurality of input keys are displayed in congestion on a prescribed position.