PURPOSE: To unnecessitate a lot of bearings and bearing supporting materials and to reduce installation cost by connecting a driving shaft of a driving source and a driven shaft of a transmission mechanism part by a flexible joint and transmitting the rotational force of the driving shaft of the driving source to the driven shaft through the flexible joint to rotate rotors.

CONSTITUTION: A rotary drum 3 is supported by plural pairs of rotors 2 consisting of a rubber tire of wheel construction. A lot of rods made of metal are housed in the rotary drum 3. The rotation of a driving shaft 5A of a driving source 5, such as an electric motor is transmitted to the rotors 2 through a transmission mechanism part 6 to rotate them, causing the rotary drum 3 to be rotated, allowing the rods to be given gyratory motion. And the driving shaft 5A of the driving source 5 and a driven shaft of the transmission mechanism part 6 are connected by a flexible joint 8, and the rotational force of the driving shaft 5A of the driving source 5 is transmitted to the driven shaft through the flexible joint 8 to rotate the rotors 2. As a result, a lot of bearings and bearing supporting materials are not required and installation cost is reduced.