Fluid machine

A fluid machine, comprising:

• a rotating body;
• an operation body rotated integrally with the rotating body;
• a housing accommodating the rotating body and the operation body;
• hydrodynamic plain bearings rotatably supporting the rotating body relative to the housing;
• and
• a cooling passage arranged in the housing, wherein a fluid directly cooling the hydrodynamic plain bearings flows through the cooling passage, wherein
• the hydrodynamic plain bearings each include a resin coating layer at a portion that is opposed to the rotating body,
• the hydrodynamic plain bearings include at least one combination of hydrodynamic plain bearings, wherein each combination includes an upstream hydrodynamic plain bearing and a downstream hydrodynamic plain bearing located at different positions in a direction in which the fluid flows through the cooling passage, and
• the coating layer of the upstream hydrodynamic plain bearing has a lower hardness than the coating layer of the downstream hydrodynamic plain bearing.