An input-output circuit sending and/or receiving a signal to and/or from an electronic device includes a driver for supplying a signal to the electronic device, a comparator provided parallel to the driver for receiving a signal from the electronic device, a relaying circuit provided between the comparator the electronic device in series with the comparator and the electronic device, a first transmission line for coupling the comparator and the relaying circuit electrically and a first switch for selecting either of short or open-circuited state of the first transmission line and the electronic device, wherein the impedance of the relaying circuit is larger than the impedance of the first transmission line.