A frame generating device includes an inserting portion and an accommodating portion. The inserting portion inserts a first fixed stuff byte and a second fixed stuff byte into a payload area of an OTU frame, the first fixed stuff byte being of (8+10n (“n” is zero or a given positive integer))×4 rows, the second fixed stuff byte being of a given byte×4 rows, the given byte being equal to zero or more and being equal to (24−10n) or more. The accommodating portion accommodates Ethernet signal in the payload area other than the first fixed stuff byte and the second fixed stuff byte.