An operation signal from a remote operation input device, e.g., a keyboard is converted into a transmission signal, and the transmission signal is output onto a communication line. The operation signal transmitted through the communication line is decoded, and the decoded signal is supplied to an input device connector of a computer. The computer having no communication function can be remotely operated upon operation of the input device. A video signal output from the computer is encoded, and is displayed on a display device arranged near the input device through another communication line. The presence/absence of a malfunction of the computer, and a malfunctioning point can be checked on the basis of an input to the input device, and a displayed image.