There is described a network facsimile apparatus, which makes it possible to quickly complete the transmitting operation of reserved image data whose transmission is temporarily suspended due to the BUSY status of the receiver side, etc. The apparatus, serving as a caller that conducts image data communicating operations with other apparatuses serving as callees based on a Session Initiation Protocol, includes a control section to suspend an operation for transmitting image data to the first callee; a storage section to store the first IP address of the first callee; a network interface control section; and a comparing section to compare the first IP address with the second IP address. When the control section determines that the first IP address and the second IP address coincide with each other, the control section transmits the reserved image data, transmission of which is currently suspended, to the second callee.