Hydrostatic pressure cylinder

A fluid pressure cylinder comprising:

• a cylinder tube including a slide hole with a circular shape inside the cylinder tube;
• a piston unit disposed to be reciprocable along the slide hole;
• a piston rod protruding from the piston unit in an axial direction;
• a magnet having a size corresponding to part of the piston unit in a circumferential direction;
• a holding member that includes a magnet holding portion configured to hold the magnet and that is attached to the piston unit;
• a rotation restriction structure configured to restrict rotation of the holding member relative to the cylinder tube;
• a first cover attached adjacent to one end of the cylinder tube;
• and
• a second cover attached adjacent to another end of the cylinder tube, wherein:
• the cylinder tube is rotatable in the circumferential direction relative to the first and second covers;
• and
• the cylinder tube is provided with a positioning portion enabling a circumferential position of the cylinder tube to be fixed with respect to the first and second covers.