A method for preparing an error map of a numerically controlled machine tool which has a linear feed axis (X, Y, Z) and a plurality of rotational feed axes (A, B, C) and in which a main spindle (4, 5) and a table are movable relative to each other, said method comprising the steps of: defining a plurality of measurement points in a movable range of said linear feed axis (X, Y, Z) and said plurality of rotational feed axes (A, B, C); attaching a cubic or parallelepiped test piece or work piece to said table; defining a reference processing surface of said test piece or work piece, said reference processing surface having X, Y, Z-axis directions as the normal, indexing the rotational feed axes (A, B, C) to a sufficiently small rotation angle as required for sufficient precision of the relative position error and the relative attitude error, and processing said reference processing surface without operating the rotational feed axes (A, B, C); for each measurement point, allotting a specified area in said test piece or work piece as an area to be processed and processing three surfaces (P15-P20) of said test piece or work piece that are orthogonal to each other with the rotational feed axes (A, B, C) indexed to the rotation angle corresponding to said measurement point; determining a relative attitude error of said main spindle (4, 5) relative to said table at each measurement point by determining a difference between actual inclinations of three orthogonal surfaces of said processed reference processing surface and three theoretical inclinations computed from the position command of the rotational feed axes (A, B, C), said actual inclinations being determined by measuring several points (P10-P14) of said processed reference processing surface with a touch probe attached to said main spindle (4, 5) and with said rotational feed axes (A, B, C) being indexed to the angle corresponding to said measurement point; determining a relative position error of said main spindle (4, 5) relative to said table at each measurement point by calculating a difference between an intersection point of three planes containing the processed surfaces (P18-P20) that are processed with the rotational feed axes (A, B, C) indexed to a reference rotation angle when it is assumed that there is no attitude error and an intersection point of three planes containing processed surfaces (P15-P17) that are processed with the rotational feed axes (A, B, C) indexed to the rotation angle corresponding to said measurement point when considering the previously determined relative attitude error; and storing said relative position error and said relative attitude error in correspondence to a position of said linear feed axis and a rotation angle of said plurality of rotational feed axes (A, B, C), in which said relative position error and said relative attitude error obtained at each measurement point compose a multidimensional error map. defining a plurality of measurement points in a movable range of said linear feed axis (X, Y, Z) and said plurality of rotational feed axes (A, B, C); attaching a cubic or parallelepiped test piece or work piece to said table; defining a reference processing surface of said test piece or work piece, said reference processing surface having X, Y, Z-axis directions as the normal, indexing the rotational feed axes (A, B, C) to a sufficiently small rotation angle as required for sufficient precision of the relative position error and the relative attitude error, and processing said reference processing surface without operating the rotational feed axes (A, B, C); for each measurement point, allotting a specified area in said test piece or work piece as an area to be processed and processing three surfaces (P15-P20) of said test piece or work piece that are orthogonal to each other with the rotational feed axes (A, B, C) indexed to the rotation angle corresponding to said measurement point; determining a relative attitude error of said main spindle (4, 5) relative to said table at each measurement point by determining a difference between actual inclinations of three orthogonal surfaces of said processed reference processing surface and three theoretical inclinations computed from the position command of the rotational feed axes (A, B, C), said actual inclinations being determined by measuring several points (P10-P14) of said processed reference processing surface with a touch probe attached to said main spindle (4, 5) and with said rotational feed axes (A, B, C) being indexed to the angle corresponding to said measurement point; determining a relative position error of said main spindle (4, 5) relative to said table at each measurement point by calculating a difference between an intersection point of three planes containing the processed surfaces (P18-P20) that are processed with the rotational feed axes (A, B, C) indexed to a reference rotation angle when it is assumed that there is no attitude error and an intersection point of three planes containing processed surfaces (P15-P17) that are processed with the rotational feed axes (A, B, C) indexed to the rotation angle corresponding to said measurement point when considering the previously determined relative attitude error; and storing said relative position error and said relative attitude error in correspondence to a position of said linear feed axis and a rotation angle of said plurality of rotational feed axes (A, B, C), in which said relative position error and said relative attitude error obtained at each measurement point compose a multidimensional error map.