PURPOSE: To provide the estimating method of the surface form of material to be cut with an inner diameter saw, by which the form, thickness and warpage of cut wafer can be grasped during cutting without actually measuring the wafer and the edge face of an ingot and, especially the form of the cut wafer can be grasped three-dimensionally and further exact data usable for controlling the displacement of the inner diameter saw and for judging the correction operation of the saw by worker or robot are obtained in the measurement of the displacement of the saw developing during the cutting of work.

CONSTITUTION: Non-contact type displacement sensors 4a, 4b and 4c arranging opposite to an inner diameter saw 1 are installed at three positions in the predetermined circumferential direction of the saw so as to calculate the displaced state of the saw 1 within work 2 on the basis of the amount of displacement obtained with the displacement sensors according to pre-set estimation equation in order to obtain a quadratic regression line passing through three points every certain period of time and store the line. Above-mentioned operation is repeated during the cutting of one wafer successively so as to three-dimensionally store the amount of displacement of the saw during the cutting of the wafer in order to calculate the deviation between the memories of one wafer and of the wafer stored before by one for obtaining the scattering in the thickness and the warpage of the wafer.