To flatly grind plane of a wide range without ruggedness and make treatment of cutting surfaces and edges easy by freely attachably/detachably providing a abrasive sheet on the bottom surface of a base material and freely attachably/detachably providing the abrasive sheet on the plane of a V-shaped groove formed along the longitudinal direction on the upper surface.

A reciprocating operation while a first abrasive sheet which is easy to be held in a state that a bottom surface 7 of the widest area which faces down and fixed to the bottom surface 7 is pressed on a surface to be ground is made easy. Because uniform pressing force is transmitted to the whole of the bottom surface 7, even the surface to be ground which has plane of a comparatively wide range is finished to uniform surface roughness without ruggedness. When the crossed angle θ of a surface 26 and a side surface 25 is about 90° and the angle of a workpiece 23 having a swelling 24 on the surface 26 side is ground, a grinding is performed by reciprocating the grinding sheet 1 from this side direction to the depth direction, hitting one plane 10 of a V-shaped groove on the side surface 25.