A verification device includes a data verifying unit that verifies whether data in a packet has an error using a first or a second verification mode, a packet generating unit that generates a packet in accordance with a first packet generation mode or a second packet generation mode respectively corresponding to the first and the second verification modes, a failure monitoring unit that monitors a failure of a transmission line that requires a switching of the verification mode, a switching packet transmitting unit that transmits to a destination device, a switching packet for informing the switching of the verification mode used by the data verifying unit when the failure monitoring unit detects a failure or a removal of a failure, a generation mode switching unit that switches the generation mode, and a verification mode switching unit that switches the verification mode to the one informed by the switching packet.