1. A display apparatus comprising: a lens for capturing light from a real world; a lens state control unit for controlling a state of said lens, the state including a focus; a storage unit for storing computer image data; a computer image generation unit for generating a computer image by using the computer image data stored in said storage unit in accordance with lens state information and the like; and a synthesis display unit for synthesizing an image captured via said lens and the generated computer image and displaying a synthetic image, wherein the focus of said lens is changed according to a position or a size where the computer image is displayed.