the radial direction in the present modification too the upper part ring 22 a and the resin ring 22 b may be fixed with each other by adhesives in the state of fig1 a while these can be fixed also by using screws 23 d as shown in fig1 b further with the present modification it is also possible to form the grooves 23 a on the resin ring 22 b and form the convex parts 23 b in the upper part ring 22 a also in the present modification fig1 a 13d show a fabrication process of a semiconductor device according to a second embodiment of the present invention that uses the polishing apparatus 10 of fig4 referring to fig1 a a silicon substrate 41 of a silicon wafer of 30 cm diameter is formed with an sin pattern 43 via a sacrificial oxide film 42 of a thermal oxide film wherein there is formed a device isolation trench 41 a in the silicon substrate 41 so as to define a predetermined device region 41 b by a dry etching process while using the sin pattern 43 as a mask next in step of fig1 b there is formed an sio 2 film 44 on the structure of the fig1 a by a cvd process so as to fill the device isolation trench 41 a and the silicon substrate 41 now in the state in which the structure of the fig1 b is formed is held on the polishing head 14 of the polishing apparatus 10 as explained with reference to fig4 6 in the step of fig1 c as the substrate 13 to be processed wherein the retainer ring 22 and the membrane 21 explained with reference to fig7 8 are used for holding the silicon.