Abstract: Data transfer is enabled according to the reception capability of each of peripherals when a plurality of peripherals is connected to a host device via common lanes. A data processing device 1 includes a host device 10 provided with an interface, a first device 12 connected to the interface via a plurality of data lanes, and a second device 13 connected to the interface via some of the data lanes. The interface adds dummy data to actual data and then assigns and transmits the resultant data to the data lanes. When the actual data is taken in one of the first device and the second device, the interface causes the other one to recognize that the actual data is meaningless. Therefore, data can be transferred to the first device 12 and the second device 13 in accordance with reception capabilities.