PURPOSE:To permit to correct the error of measurement of a probe and obtain highly accurate working dimension by a method wherein the dimensional error of the tip end pole of the probe is being measured previously in accordance with a contacting direction and a measured value is corrected upon a measurement under a program. CONSTITUTION:Radii in the directions of +-X, +-Y and Z are measured previously from the tip end of the probe 3, the data are inputted from a key board 8 into a register 11, the dimensions on a drawing are preset into the register 12 and a cutting procedure, condition and an M code for measurement are programmed into an NC tape. The NC tape is read by a numerical control unit 1 and the M code for measurement is decided. Next, measuring reference points in the X, Y, Z axes of a work piece are measured by the measuring program and when the probe 3 contacts with the work piece on the way of movement to a subsequent measuring point, a latch signal is outputted, said signal is inputted into a conroller 5 to hold present position data and is sent to the register 13 of the control unit. Here, an operation is effected by an operator 16 to feedback it into the control unit 1 and provide it as the working condition.