Abstract: An image transmission apparatus which is capable of self-diagnosis automatically and successively and which is also capable of automatic system recovery In one embodiment, self-diagnosis may be instructed from a remote station. A reference video signal generated by a pattern generator is supplied to return loops and the return data and the original video signal are compared with each other in a pattern diagnostic circuit. The results of the diagnosis are displayed on a diagnosis result panel. A self-diagnosis start instruction is given from an external circuit and the diagnosis result is transmitted over the line. A change-over switch switches the working and backup circuit systems of the sending and receiving sides responsive to the diagnosis result.