To simplify a structure according to the technical drawing from a structural technical drawing because much time and labors are required for determining the quantity of steel necessary for constructing the structure.

A method in which a computer reading, analyzing and interpreting the structural technical drawing is used for determining the quantity and shape of steel used for construction according to the structural technical drawing is provided. The method contains a line and a symbol displaying a steel bar and discrimination, analysis and interpretation by processing at a plurality of stages of relationship among these line and symbol, and processing at a plurality of stages comprises the discrimination, analysis and interpretation of an indication line, the discrimination of the shape of the steel bar and a spatial constitution and the determination of the size of the steel bar by a pair of previously demarcated values and an algorithm.