PURPOSE: To enable the honing work for the plane such as the inner surface of the square hole of a workpiece.

CONSTITUTION: A work W is reciprocatingly shifted in the horizontal direction which crosses with the axis line at right angle and parallel to a plane Wa, holding a work W so that the axis line X is directed in the vertical direction, by a work holding device 2, and the grinding wheels G and G of a horning tool 1 are bulged outward for the plane Wa of the work W through the reciprocating operation in the vertical direction along the axis line X of the work W. Accordingly, the honing work for the inside plane Wa is carried out, maintaining the similar relation to the honing work technique for the conventional cylinder inner surface, between the work W and the grinding wheel G.