There are included a control unit configured to, when detecting that no high priority traffic frame arrives for a frame interval threshold or longer in the period that allows high priority traffic frames to be transmitted, release the period that allows high priority traffic frames to be transmitted and allocate the released period to the period that allows low priority traffic frames to be transmitted, a frame arrival time information acquisition unit configured to obtain information of frame arrival times of high priority traffic frames, a frame interval calculation unit configured to calculate, in accordance with the information of frame arrival times obtained by the frame arrival time information acquisition unit, frame intervals between frames of the high priority traffic frames input in chronological order, a frame interval threshold calculation unit configured to calculate a new frame interval threshold in accordance with the frame intervals, and a frame interval threshold configuration unit configured to change the frame interval threshold to the new frame interval threshold.