A fax data transmission device receives fax data, and stores it together with an identifier for identifying the fax data. The fax data transmission device sends receipt information which includes the identifier and a notification that the fax data identified by the identifier has been received, to an external device. The fax data transmission device receives destination information relating to a destination to which the fax data should be forwarded, as a reply to the receipt information. The fax data transmission device sends the fax data to the destination specified based on the destination information.