To facilitate insertion or pulling-out of a corrugating roll unit into/from a single facer, and to eliminate the necessity of a wide space around the single facer.

The corrugating roll unit 1 including a pair of corrugating rolls 3 and 4 mounted and secured to a truck 2 having traveling wheels 12 and 14 and attached to/detached from the operation part of a single facer s is constructed in such a manner that two spare wheels 24 having traveling directions set in the horizontal direction of the truck 2 and attaching positions changeable up or down from the rear wheel 14 are disposed near the rear wheel 14, the spare wheels 24 are lowered from the wheel 14 during turning of the corrugating roll unit 1 or movement in a horizontal direction e, the corrugating roll unit 1 is made to travel by the front wheel 12 and the spare wheels 24, the spare wheels 24 is made to travel in the opposite direction of the front wheel 12 during turning of the corrugating roll unit 1, and by adjusting a space between the front wheel 12 and the spare wheels 24 or the traveling speeds of these wheels, the turning center c of the corrugating roll unit 1 is set in an optional position between the front wheel 12 and the rear wheel 14.