To assuredly support an exhaust branch pipe even when a cylinder cover is detached in maintenance.

Cylinders are arranged in a V shape and one main air supply pipe 24 and two main exhaust pipes 25 are disposed along the arranging direction of the cylinders 22. To the main exhaust pipe 25 between adjacent expansion pipes 29, one end of an exhaust branch pipe 28 of each cylinder 22 is integrally connected. The other end of each exhaust branch pipe 28 is connected to the cylinder cover 23 so as to be detached therefrom. To the main air supply pipe 24, one end of an air supply branch pipe 27 of each cylinder 22 is connected. The other end of each air supply branch pipe 27 is connected to the cylinder cover 23 so as to be detached therefrom. Further, the other end of each exhaust branch pipe 28 is connected to the other end of the air supply branch pipe 27 of the same cylinder by a connecting member 35 to support the exhaust branch pipe 28 by the air supply branch pipe 27.