To prevent delay for rewriting a display screen by changing a transmitting method of drawing information to a display apparatus according to a screen rewriting amount, while duplicating appearance of a screen displayed on a personal computer as much as possible on the display apparatus such as a projector.

An image to be sent to the projector is acquired from a drawing instruction to OS and the drawing instruction is stored as an image data and a range data, and based on the data, image information is generated and sequentially transmitted. When the delay more than a permissible value is generated in transmission, the range of screen which is rewritten in the past is specified from the range data indicating rewriting range and the latest screen information is acquired from a buffer for screen displaying about the specified range and transmitted.