<p>Provided is a fluid machine comprising a cylinder (21) including an outer cylinder member (24) and an inner cylinder member (25) formed on the front face of an end plate (26) thereby to form annular cylinder chambers (C1 and C2). Further comprised is a piston (22) including an annular piston member (22a) formed on the front face of an end plate (16c) and housed in the cylinder chambers (C1 and C2) eccentrically of the cylinder (21). In the cylinder (21) on the back side of the end plate (26), there is formed an annular back pressure chamber (53), which communicates with the cylinder chamber (C1) in an intermediate pressure state thereby to push the cylinder (21) under the intermediate pressure to the piston (22). With the back pressure chamber (53), moreover, there communicates an oil passage (55) for guiding the oil to fill up the back pressure chamber (53).</p>
