An air pressure adjustable elastic body is integrally formed with an inflation/deflation module on a joining member which is formed by plastic injection molding. With the inflation/deflation module, the user can adjust the air pressure in the elastic body as desired, improving the application of the elastic body. Furthermore, since all components of the elastic body are formed by the plastic injection molding, the manufacturing procedure can be simplified, reducing the production cost while enhancing the economic benefit. In addition, since the elastic body is formed by the integral injection molding, it has no structural defects.