A method for recalibrating a non-contact sensor in a CNC processing apparatus , wherein the CNC processing apparatus is configured to process an object with a tool, replace the tool mounted on a spindle of the CNC processing apparatus with a sensor head , the sensor head comprising a holder for mounting the sensor head on the spindle and the non-contact sensor , and measure a surface shape of the object with the non-contact sensor , comprising: a first step of measuring center coordinates of a reference instrument with a contact probe mounted on the spindle and thereby determining coordinates in a machine coordinate system of the center of the reference instrument, a second step of, after mounting of the sensor head onto the spindle , whereby the holder is rotatable about a Z-axis, but cannot move in X-axial, Y-axial and Z-axial directions and cannot rotate about an X-axis and a Y-axis, measuring the center coordinates of the reference instrument only one time with the non-contact sensor , and thereby determining coordinates in a non-contact sensor coordinate system of the center of the reference instrument, a third step of calculating to determine an angle about the Z-axis (Zθ1) and offsets in the X-axial, Y-axial and Z-axial directions (X1, Y1, Z1) required to bring the coordinates in the non-contact sensor coordinate system obtained in the second step into agreement with the coordinates in the machine coordinate system obtained with the contact probe in the first step, and adding the angle about the Z-axis (Zθ1) and offsets in the X-axial, Y-axial and Z-axial directions (X1, Y1, Z1) calculated above to angles about the X-axis, Y-axis and Z-axis (Xθ0, Yθ0, Zθ0) and offsets in the X-axial, Y-axial and Z-axial directions (X0, Y0, Z0) calculated in a first calibration of the non-contact sensor performed before an object processing. a first step of measuring center coordinates of a reference instrument with a contact probe mounted on the spindle and thereby determining coordinates in a machine coordinate system of the center of the reference instrument, a second step of, after mounting of the sensor head onto the spindle , whereby the holder is rotatable about a Z-axis, but cannot move in X-axial, Y-axial and Z-axial directions and cannot rotate about an X-axis and a Y-axis, measuring the center coordinates of the reference instrument only one time with the non-contact sensor , and thereby determining coordinates in a non-contact sensor coordinate system of the center of the reference instrument, a third step of calculating to determine an angle about the Z-axis (Zθ1) and offsets in the X-axial, Y-axial and Z-axial directions (X1, Y1, Z1) required to bring the coordinates in the non-contact sensor coordinate system obtained in the second step into agreement with the coordinates in the machine coordinate system obtained with the contact probe in the first step, and adding the angle about the Z-axis (Zθ1) and offsets in the X-axial, Y-axial and Z-axial directions (X1, Y1, Z1) calculated above to angles about the X-axis, Y-axis and Z-axis (Xθ0, Yθ0, Zθ0) and offsets in the X-axial, Y-axial and Z-axial directions (X0, Y0, Z0) calculated in a first calibration of the non-contact sensor performed before an object processing. <EOS>