To surely check and detect a stroke end, etc., by detecting the fluid through communication with the inside of a cylinder in which the fluid is introduced when a sliding piston end face reaches the predetermined position.

Cylinder cut-holes 22, 23 leading to detecting means 25, 27 when a piston is in an intermediate position, is in a closed condition by a piston 12. In this condition, the hydraulic force is generated in a hydraulic chamber 13(14) by supplying the hydraulic pressure from inlets 17(19) of a first (second) hydraulic system of the cylinder 11, and the piston 12 is advanced (retracted). The oil in the hydraulic chamber 14(13) is discharged from inlets 19(17). When the piston 12 reaches the advancing (retracting) end, the hydraulic chamber 13(14) communicates with the cylinder cut-holes 22(23), and the hydraulic force is generated inside a conduit 24(26) leading to detecting means 25(27), or a large volume of outflow oil is discharged. The change in the hydraulic force or the oil outflow is detected by detecting means 25(27) to check that the piston reaches the advancing (retracting) end.