Abstract: A fax machine equipped for simultaneous transmission and reception via two telephone lines. The fax machine is provided with a master processor, a slave processor and a command buffer, in which the master processor is communicated with a first remote fax machine and the slave processor is communicated with a second remote fax machine via respective telephone lines. The command buffer is interposed between the master and slave processors to provide a transmission channel for the command signals. An image buffer is connected to the master processor via a first switch, and is connected to the slave processor via a second switch to store image data at the request of the master processor when transmitting the image data to the second remote fax machine and to store image data at the request of the slave processor when receiving the image data from the second remote fax machine.