A backgrinding machine 10 of a semiconductor wafer W includes: a table 13 set on the working plane of a mount 11; a multiple number of holding jigs 20 arranged via check tables 15 on table 13; a grinding machine 30 for performing a grinding process of the rear side of semiconductor wafer W held by holding jig 20; and a washing device 40 for ground semiconductor wafers W. Each holding jig 20 is constructed of a concave 22 depressed on the surface of a base plate 21, a multiple number of supporting projections 23 projectively arrayed on the bottom surface of concave 22, a deformable contact film 24, covering the concave 22, being supported by the multiple supporting projections 23, for detachably holding semiconductor wafer W in close contact with it; and an exhaust path 25 for conducting air from the concave 22 covered by contact film 24 to the outside.