Abstract: 
A method of accurately measuring the size of a mold, by using a laser measuring instrument. The method comprises a first step of directing a laser emission portion of a laser measuring instrument to the inner surface of a first corner portion of the corner portions of a mold whose size is to be measured, at a suitable angle of inclination, moving the laser measuring instrument relative to the mold in a direction substantially parallel to the mold surface so as to continuously measure the portion near the first corner position, expressing two arbitrary measurement values inside a first measurement surface using xy coordinates on the basis of the measurement values relating to the first corner portion among the measurement values so obtained, determining a relational formula between these two coordinates values as a regression line by the method of least squares, similarly determining a relational formula relating to the xy coordinates values of two arbitrary measurement values on a second measurement surface which forms the corner portion with the first measurement surface as a regression line by the method of least squares and calculating the intersection of these two regression lines as the first corner position, a second step of calculating the second corner position in the same way as the first step, and a third step of calculating the distance between the first and second corner positions.
