A bearing raceway ring (25) disposed near a mounting section (9) is disposed on the outer periphery of a circular cylinder section (19). A fluid-sealed chamber (40) in which a measurement liquid is hermetically enclosed is provided between a first member (8) and the bearing raceway ring (25) which is disposed near the mounting section (9). Pressure acting on the fluid to be measured changes as the bearing raceway ring (25) moves in the cylinder-axis direction, the bearing raceway ring (25) being disposed near the mounting section (9). The fluid-sealed chamber (40) is provided with a pressure sensor (44) capable of detecting a change in the pressure of the fluid to be measured.