Since structural portions of a device made of a plurality of materials are different from one another in mechanical hardness, it is very difficult to uniformly lap the structural portions. This is attributable to generation of machining recessions due to differences in lapped amount when large fixed abrasive grains are used, and generation of lapping marks caused by that the dropped abrasive grains rotate. Accordingly, in order to cope with the disadvantage, it is essential to surely grip abrasive grains of small size to a surface of a surface plate.[Solving Means]Abrasive grains are fixedly forced into a surface of a lapping tool with mechanical pressure and then the surface of the lapping tool including the abrasive grains is subjected to plasma processing, whereby an improvement in adhesion between the abrasive grains and a surface plate and reduction in the number of loose abrasive grains, which are dropped from the surface of the lapping tool, can be achieved, so that it is possible to realize lapping, in which a surface of a device made of a plurality of materials is made very plane.