PURPOSE: To facilitate the grinding even when the grinding wheel surface is flat as well as when the grinding wheel surface is curved by forming a universal joint consisting of body to be inserted, a base plate and the grinding wheel.

CONSTITUTION: A semi-automatic grinding device consists of a body 2 to be inserted and a base plate 4, arm rods 3a, 3b are vertically provided at the lower end part of the body 2 to be inserted in a right-to-left symmetric manner, a connector 6 is interposed between the arm rods 3a, 3b to be pivotably supported by the arm rods 3a, 3b, and projections 5a which are projected on the base plate 4 with the prescribed space therebetween are provided opposite to each other between the arm rods 3a, 3b and pivotably supported by the connector 6, forming the universal joint.