hard transparent plastic material scale member 44 has a scale 41 within scale member 44 there is provided a bellow member 42 bellow member 42 is formed of strong elastic material having its wavy peripheral section 43 urged against the inner periphery of scale member 44 by the pressure of air 5 of tire 2 also top of bellow member 42 may lift or lower due to the nature of elastic material as the pressure of air 5 of tire 2 changes in use prior to driving driver can know the pressure of tire 2 by observing the top of bellow member 42 which is aligned with a certain scale 41 referring to fig3 a pressure indicating device 6 of a second preferred embodiment mounted on a valve is shown pressure indicating device 6 comprises a base 61 consisting of an inner hollow cylinder 611 having an inner threaded section being secured to outer threaded section of valve and an outer hollow cylinder 612 with bottoms of cylinders 611 and 612 coupled together as a closed section and tops thereof open thus forming a space 614 between cylinders 611 and 612 a helical spring 62 put on inner hollow cylinder 611 having a lower end rested on bottom of base 61 a hollow disk shaped seal 63 put on inner hollow cylinder 611 being.