Abstract: A pressure gauge has a base, a control knob, a pressure detector, a display and a cover. The base has a chamber, an inlet tube, an outlet tube and a controlling tube. The controlling tube has an inner end protruding into the chamber of the base and communicating with the inlet tube. The control knob is mounted rotatably on the controlling tube to open or close a communication between the inner end of the controlling tube and the inlet tube. The pressure detector is mounted in the chamber to detect air pressure in the base. The display is mounted in the chamber of the base and is connected electrically to the pressure detector to display the air pressure detected by the pressure detector. The cover is attached detachably on the base to close the chamber and has a window from which the display is exposed.