Abstract: An axial flow fluid compressor including a casing, a cylinder mounted in the casing, a rotary member arranged in the cylinder so as to extend along the axis of the cylinder and be eccentric to the cylinder and rotatable relative to the cylinder while part of the rotary member is in contact with the inner surface of the cylinder along a line longitudinal to the axes of the cylinder, the rotary member having a pair of spiral blades movable in the radial direction of the rotary member so as to define two sets of working chambers having volumes gradually decreasing from a suction-side to a discharge-side, a power transmission for relatively rotating the cylinder and the rotary member to successively transport a fluid introduced from the suction-side toward the dischage-side through the working chambers, a pair of bearings for supporting respective ends of the rotary member, and a pair of openings formed at the respective ends of the rotary member for applying the pressure of the fluid in the cylinder to the pair