Abstract: Disclosed is a gas cylinder type height-adjusting apparatus of a swivel chair which has a simple structure and thereby can be manufactured at a low cost. In the apparatus, an actuating pin opens an orifice so that working fluid can flow from the first chamber through the second chamber into the third chamber when the actuating pin is pressed down, while the actuating pin blocks up the orifice when the actuating pin is not pressed down. The orifice is formed in an actuating pin socket manufactured by coating synthetic resin after an integral single forming of a single material. The first chamber is defined by an alternating piston which is manufactured by coating synthetic resin after an integral single forming of a single material. The shaft bearing member has a shape of a single annular ring whose upper and lower surfaces are curved surfaces curved with a predetermined curvature or tapered surfaces tapered at a predetermined angle.