PURPOSE: To increase the measuring accuracy of the machining components of force in the two directions described below and a normal direction by providing through holes in the axial direction or transverse direction in a holding part of a tool which is contacted with a work which is rotated around the axis and moves in the axial direction.

CONSTITUTION: The tool 1 which can be moved freely in the axial direction of the work 6 which is rotated around the axis of a mandrel of a lathe is supported by a tool stand 5 by way of a machining component measuring part 3. The tool 1 is compressed to the work 6 and moved in the axial direction to perform the spinning of flow forming. The configuration of the machining component measuring part 3 is rectangular so that the thickness in the sending direction X of the tool 1 is thick, and the thickness in the transverse direction Z at the contact point of the tool 1 and the work 6 is thin. The through holes 4 and 4 in the rectangle, whose long sides are aligned with the normal direction Y at said contact point, are provided in the direction Z. Strain gages GXWGZ which measure the component in each direction are stuck to the positions in the Figure. The sensitivity levels in the three directions become approximately equal, and the accurate machining components can be obtained.