The present invention discloses a machining error calculation apparatus for calculating the machining error more precisely through analysis. The apparatus comprises: a tool center displacement amount calculation part for calculating a displacement amount of a rotation center of the rotation tool according to the cutting resistance force in the rotation tool, in the case that the cutting resistance force generated in the rotation tool during said interrupted cutting is varied; a relative tool-edge position calculation part for calculating a relative tool-edge position of the cutting-edge portion with respect to the rotation center of the rotation tool; an absolute tool-edge position calculation part for calculating an absolute tool-edge position of the cutting-edge portion with respect to the workpiece, based on the displacement amount of the rotation center of the rotation tool and the relative tool-edge position; a machined shape calculation part for calculating the machined shape of the workpiece through transferring the absolute tool-edge position on the workpiece; and a machining error calculation unit for calculating a machining error of the workpiece based on a difference between the machined shape of the workpiece and an objective shape of the workpiece.