PURPOSE: To extend the using range of general purpose engineering plastic, used in a fluid machine casing made of resin, to a high temperature area of 80°C or more.

CONSTITUTION: Ribs 5 the radiation area of which is sufficiently increased are arranged in a bamboo basket mesh-form manner on the outer surface of a casing 6 on which temperature and a fluid pressure are exerted. The height of the rib is designed such that temperature is kept at a value approximately equal to an atmospheric temperature at the tip of the rib spaced farmost away from a casing body. The ribs are arranged at the wall of the casing surrounded with ribs base bottoms such that an area is set to a value enough to allow slight deformation even at a high temperature area and the casing is durable to all forces generated by an internal pressure exerted on the casing 6 by means of the strength of only the ribs 5.