As measurement accuracy required for the scanning electron microscope (SEM) for measuring a pattern width becomes stringent, a technique of reducing the difference in a measured dimension between the SEM's is desired. However, the conventional technique of evaluating the difference in a measured dimension between the SEM's cannot separate the difference in a measured dimension between the SEM's themselves and a dimensional change resulting from deformation of the pattern itself. Moreover, the technique of reducing the difference in a measured dimension between the SEM's needs an operator for reducing the difference in a measured dimension between the SEM's for each measurement pattern shape. In this invention, a pattern at the same position is measured for a plurality of times with each SEM, and a different between extrapolated values of measured values obtained by the respective SEM's is calculated, whereby separation between the difference in a measured dimension between the SEM's and a dimensional change resulting from deformation of the pattern itself is made possible. Moreover, matching electron beam image profiles between the SEM's using an operator that simulates a difference in beam diameter between the SEM's makes it possible to reduce the difference in a measured dimension between the SEM's, not depending on a dimensional measurement pattern shape.