Adjustment method of a machine tool, and a machine tool

In ultra-precision machining by a machine tool, which provides an adjustment method of a round bar-like workpiece (W) is rotatable while suppressing runout of the shaft center. In the axis position adjustment procedure (S5), while rotating the workpiece spindle (40), to measure the side surface of the projecting portion of the holding state by the work holding mechanism (50) work (W). Adjust the C-axis adjustment screws (42b) so that runout of the workpiece (W) is minimized, to fix the position of the workpiece axis (C2). Support Adjustment Procedure (S6), while fixing the position of the workpiece axis (C2), to adjust the workpiece (W) so as to support the support block (91). Support lock procedure (S7), by pressing the workpiece (W) by work holding (92), to maintain the prescribed position of the workpiece axis (C2) by the support block (91). In the floating restriction canceling procedure (S8), to release the floating restriction by the C-axis adjustment screws (42b).