An image forming apparatus, wherein a SOAP processing section determines, when a communication processing section receives a document data request message from a client apparatus, whether a request message for causing an image reading apparatus to read a document image and to generate document data and requesting transmission of the document data or a request message for requesting transmission of the document data within a document box is represented by the document data request message, generates a response message containing the document data corresponding to the document data request message, and causes the communication processing section to transmit the response message to the client apparatus.