A lifting-arm type round bale trailer was designed, built, evaluated for its working rate. The round bale trailer employs 4 lifting arms to load 4 round bales. Each lifting arm consists of 4 round pipes that are arranged to distribute the pressure on the surface of the bales. Two pipes called pickup pipes perform the opening and closing operations. The structure and mechanism enable to load and unload wrapped bales without injuring the film stretched on them. All the operations are easily controlled from the tractor. The operation time required for the transportation of the bales by the trailer was measured, and compared with that of the fount-end loader of a farm tractor. Loading and unloading times required by the trailer were remarkably short, and less than one-fourth of the operation time required by the loader. On the basis of the operation time, the working rate for the transportation of the bales in relation to the traveling distance was estimated. The results showed that the trailer was more efficient than the truck for loading 7 bales within a 1.5 km distance.