An image forming apparatus that uses a Web application and is capable of performing image processing without delay and reducing power consumption. The image forming apparatus communicates with a Web server. A scanner unit reads an image, and a printing unit prints the image. Power is supplied to at least one of the scanner unit and the printing unit. A user interface unit displays an operating screen based on data transmitted from the Web server, and based on the data, power is supplied selectively to the scanner unit or the printing unit.