To provide a data repeating device mounting a filtering circuit which discards a short frame (short packet) shorter than 64 byte from the Ethernet (trade mark) and does not transmit the short frame to the WAN side.

When a frame being processed currently is referred to a current frame and the data part of the current frame is smaller than a minimum data size, a data size detection unit (14) generates transfer prohibition instruction. In response to the transfer prohibition instruction, a write memory address generation unit (15) specifies a write memory address for overwriting the data part of the current frame stored in a memory block (12) with the data part of a frame next to the current frame.