To enable simpler dimensional control of clearances between each rotary valve and each annular sliding surface.

A cylinder 21 and a piston 8 are combined to construct a fluid pressure chamber 25, an inflow passage 2b and an outflow passage 1b are communicated with the fluid pressure chamber, and the inflow passage and the outflow passage are opened onto the annular sliding surfaces 1d, 2d, respectively. With the rotary valves 23, 24 rotated inside the annular sliding surfaces in linkage with the linear reciprocating motion of the piston, the inflow passage is opened and the outflow passage is closed when the piston carries a fluid into the fluid pressure chamber, and the outflow passage is opened and the inflow passage is closed when the piston carries the fluid out of the fluid pressure chamber. The rotary valves have annular valve elements for opening/closing the inflow passage and the outflow passage while inscribing the annular sliding surfaces, and resin plates 23c, 24c of the valve elements are always biased in the outer peripheral directions to change their outer diameters depending on clearances to the annular sliding surfaces, respectively.