PURPOSE: To reduce the wt. of a product without generating a sink by injecting a dicyclopentadiene resin into a mold and rotating the mold to perform rotation molding.

CONSTITUTION: A turntable 30 is attached to the upper end part of the inner pipe shaft of a rotary shaft 34 having a double pipe structure and the leading end part of a right-angled V-shaped rotary arm 35 is connected to the upper end part of the outer pipe of the rotary shaft 34. The root part of the rotary arm 35 is connected to the leading end part of the outer pipe shaft 37 of a rotary shaft 36 having a double pipe structure and the root part of the outer pipe shaft 37 is connected to the output shaft 38 of a motor M1 through a gear. When the output shaft 38 is rotated by the motor M1, the outer pipe shaft 38 is rotated through a gear and the rotary arm 35 is rotated to vertically rotate the mold 20 placed on the turntable 30 around the main axis α of the rotary shaft 36. Therefore, the wt. of a dicyclopentadiene resin product produced by rotation molding is reduced.