A user interface generation device includes: a generation unit which generates a user interface for instructing an execution unit to execute a function based on an application program; and a storage unit which stores a definition file defining a user interface object and information indicating a display ability of a display unit. The generation unit selects or discards the object definition information and judges whether all the objects can be displayed. If No, the generation unit rewrites the information relating to the object size according to the information in the display unit so that all the objects can be displayed. After this, the generation unit generates a synthesis user interface according to the information.