1. A user terminal device comprising: a display unit for displaying an output result of a web application process; a video output memory unit for storing the output result displayed on the display unit; a memory unit for storing data including an intermediate operation result according to a process of a processor unit; and the processor unit for executing processes including the web application process, parsing a provided web document created in a web description language and converting into a DOM tree data having a structure formed in a shape of a tree, creating a render tree data having a structure the same as that of the converted DOM tree data, in which non-output nodes excluding display output nodes corresponding to data that will be output on a display means are configured as void nodes, storing the render tree data in the video output memory unit, and providing the render tree data to the web application process.