1. A user interface generation apparatus comprising: an application program execution unit for implementing a variety of functions based on an application program; a user interface generation unit for generating a user interface for instructing the application program execution unit to execute a predetermined function based on the application program; a memory unit for storing a user interface definition file including user interface object definition information for defining a user interface object, which is a component of the user interface; and a selection screen generation unit for generating a selection screen for receiving selection of the user interface object based on the user interface object definition information, wherein the selection screen generation unit, if it is instructed to compound a plurality of user interfaces, generates the selection screen based on the user interface object definition information included in the user interface definition file stored in the memory unit correspondingly to each of the plurality of user interfaces instructed, and the user interface generation unit generates a compound user interface definition file including user interface object definition information of user interface objects selected on the selection screen, and generates a compound user interface based on the compound user interface definition file.