To reduce a use amount of working fluid without reducing a quality by providing a gas jetting-out means for jetting-out gas so as to cause working fluid supplied from a working fluid supplying means to enter a contact part between an operation element and a workpiece.

The flow of grinding water 15 is strengthened by jetted-out air 14, and forcibly enters even a small gap in a contact part between a semiconductor wafer W and a grinding wheel 48. By this entered grinding water, together with the generation of vaporization heat by the vapovigation of the grinding water, the cooling of the semiconductor wafer W is further promoted. Even if the supply amount of the grinding water is only 0.4 lit./min., which is 1/5 of a conventional amount, the cooling of the semiconductor wafer is promoted by the jetting-out of air, and the surface burning of the semiconductor wafer W becomes difficult. Also, grinding distortion or cracks are difficult to occur, surface roughness is eliminated and mirror-face grinding is allowed. Further, even if the rotational speed of a spindle 42 is reduced, thin grinding is performed so as to set the thickness of the semiconductor wafer W to, for instance 200 μm or less.