PURPOSE: To enable speed detection with a simple constitution by providing a planar board along a stator and attaching a movable member having a function of fluid sliding bearing opposite to said board via a pressure sensor to a movable element.

CONSTITUTION: A planar board 4 is provided along a stator. A movable member 5 opposed to said board 4 and forming an inclined plane having a pressing angle in the direction of movement of a movable element to the board 4 is attached to the movable element via a pressure sensor 6. When the movable element, or pressure sensor 6 and the movable member 5 move, air between the movable member 5 and the board 4 is compressed and a force is generated in the movable member 5 as a reaction against said air compression. Said force is proportional to a speed of the movable member 5 and converted into an electrical signal by the pressure sensor 6.