A transmission device includes: a first interface unit to receive data of a plurality of first paths transmitted corresponding to a first data stream and outputting the data per path; a second interface unit to receive data of a plurality of second paths transmitted corresponding to the first data stream and outputting the data per path; a switch unit to input the data which has been output from the first and second interface unit and select and output the data from the first interface unit or the data from the second interface unit per path; a phase detection unit to detect and output a phase difference among the paths of the data which has been output from the switch unit per path; and a control unit to control the switch unit on the basis of the detected phase difference.