A shaft and a rotary valve, which are formed integrally, are made of an iron-based metal while a cylinder block is made of an aluminum-based metal. A sleeve forms a slide surface between the cylinder block and the rotary valve when the shaft and the rotary valve rotate together. The sleeve has a coefficient of thermal expansion closer to those of the shaft and the rotary valve than that of the cylinder block. This structure prevents an increase in the clearance between the housing and the rotary valve due to the increased temperature at the time the shaft rotates at a high speed, and prevents gas leakage and a reduction in sealability. |