To provide a gateway device reducing a communication load on a bus line and enabling stable communication.

The on-vehicle gateway device has: a reception buffer temporarily storing a frame received from a first or second bus line for each kind of frame; a transmission buffer temporarily storing a frame transmitted to the second or first bus line; and a transmission means for transmitting the frame temporarily stored in the transmission buffer to the second or first bus line for a prescribed period. In this case, a plurality of kinds of frames temporarily stored in the reception buffer are rearranged in a single frame, and the single frame is stored in the transmission buffer.