To easily and safely execute works for installing sheathing roof boards on purlins.

A movable carrier 9 is equipped with a carrier main body 10 for carrying sheathing roof boards, a plurality of sliding rollers 13a or 13b attached to the underside of the carrier main body 10 from its side A to the other side B at intervals approximately equal to intervals of purlins, engaging rollers 15 attached to the carrier main body 10 on positions close to the sliding rollers 13a positioned near the side A of the carrier main body 10 and being adjoined to and in intersecting at a right angle the sliding rollers 13a, and a support member 17 provided in upward projection at a position near the other side B of the carrier main body 10. When the movable carrier 9 is placed on the plurality of purlins, the sliding rollers 13a or 13b become capable of sliding over the surface of the purlins while the engaging rollers 15 become capable of being engaged slidably with the upper lateral of the purlin placed in the uppermost position.