A method for calibrating a CNC processing apparatus is provided that can significantly reduce the amount of operation time required for sensor calibration. A method of the present invention for calibrating a non-contact sensor in a CNC processing apparatus 1 includes a first step, a second step and a third step. In the first step, the center coordinates of a reference instrument are measured with a contact probe and thereby the machine coordinates of the center of the reference instrument are determined. In the second step, after a non-contact sensor 110 is mounted onto a spindle 26, the center coordinates of the reference instrument are measured only one time with the non-contact sensor 110, and thereby the non-contact sensor coordinates of the center of the reference instrument are determined. In the third step, calculations are made to determine the amount of displacement required to bring the non-contact sensor coordinates obtained in the second step into agreement with the machine coordinates obtained with the contact probe in the first step.