An image communication apparatus is provided which is capable of transmitting images using network addresses corresponding to telephone numbers derived from a plurality of telephone systems.The image communication apparatus for use in the image communication network system containing a computer network, inside telephone network, outside telephone network, first address supplying device to store correspondence between inside numbers and network addresses and a second address supplying device to store correspondence between outside telephone numbers and network addresses, is provided with a judging section to judge whether an input telephone of another facsimile can be used, an address receiving section receives network addresses corresponding to input telephone numbers from either of both address supplying devices based on judgment of the judging section and an image transmitting section to transmit images through computer networks to the another image communication apparatus based on network addresses.