PURPOSE: To obtain a proper evaluation data in the controlling of a shape based on an evaluation index by performing an approximation for a degree of steepness measuring data measured by a curve according to a polynomial of four orders or more to accomplish the evaluation of the shape accurately.

CONSTITUTION: The degree of width-wise steepness measured data of n measured by a shape detector are used to perform an approximation according to a polynomial of specified four or six orders. In the converting of the resulting coefficient to a shape evaluation index, a peak value of a shape is defined as an equivalence peak value, as viewed from a relationship of the peak value and an effective value when the shape is regarded as comprising a sine wave or a synthetic wave containing a higher order component. Then, symmetrical components and non-symmetrical components are plotted on an evaluation plane to evaluate the shape from the length and the phase of a vector. This enables accurate evaluation of the deficiency in the shape as caused in the actual process even when the shape is complicated thereby obtaining an evaluation index corresponding even to an evaluation method in off line as in the past.