PURPOSE: To improve finishing precision as well as shortening finishing time at the time of grinding the vertical surface of a workpiece by a grinding wheel with an axis concerning a machine tool furnished with a vertically moving main spindle stock and a horizontally moving table to place the workpiece on it.

CONSTITUTION: A first main spindle stork 21 is provided on a machine main body 1, a second main spindle stock 22 is provided on this first main spindle stock 1 and a main spindle 8 is provided on this second main spindle stock 22. The first main spindle stock 21 moves vertically against the machine main body 1, and the second main spindle stock 22 moves vertically against the first main spindle stock 21. At the time of grinding the vertical surface, the second main spindle stock 22 is vertically oscillated at high speed against the first main spindle stock 21. At the main spindle stocks 21, 22 are made in two steps, a grinding wheel with an axis is vertically oscillated at high speed. Consequently, it is possible to shorten finishing time and to improve finishing precision.