To provide an IrDA controller that can make communication by with optimum procedure without collision of commands even under an environment where host devices and peripheral devices are in existence.

The host device is provided with a host side back-off value setting means that sets a back-off value of the host device, a decision means that decides transmission timing of a response command in response to a command received from the peripheral device and to which no destination host device is designated, and an inhibition means that inhibits the transmission of the response command when other devices are on the way of a series of Enumeration processing, and the peripheral device is provided with a peripheral device side back-off value setting means that sets a back-off value of the peripheral device, a decision means that decides transmission timing of a response command in response to a command received from the host device and to which no destination peripheral device is designated, and an inhibition means that inhibits the transmission of the response command when other devices are on the way of a series of Enumeration processing.