A pressure sensor which detects delicate changes in pressure as small as 0.01 .mu.m water column by detecting displacement or torque in a movable plate. The sensor comprises a fixed plate in which slits are formed, a movable plate on which pressure to be measured is impressed, a supporting member which supports the movable plate at two points on a straight line passing through its center of gravity so as to enable the movable plate to rotate thereabout, and a detecting means for detecting displacement or torque in the movable plate. The different pressures act on the movable plate to cause the rotation thereof and the displacement or torque so that such displacement corresponds to the pressure difference.