Abstract: A tire testing device includes a road surface, a carriage capable of traveling along the road surface in a state where a test tire is in contact with the road surface, and a guide mechanism configured to guide movement of the carriage. The guide mechanism includes a rail, and a runner. The runner includes a first roller that rolls on an upper surface of a head of the rail, and a second roller that rolls on a lower surface or a side surface of the head of the rail. The tire testing device includes a first guide mechanism and a second guide mechanism. In the first guide mechanism, the rollers except for the first roller are disposed only on one side of the rail, and in the second guide mechanism, the rollers except for the first roller are disposed only on an other side of the rail.