PURPOSE: To estimate the life of a sawtooth edge by automatically determining the consumption rate of the sawtooth edge when a work piece is cut or the cross section area of the work piece to be cut next which can be cut before the end of the life.

CONSTITUTION: The consumption coefficient Cn for each material of a work piece W is filed in a consumption coefficient file 115 in advance, the reference cross section area A of the reference material of the work piece W before the end of the life is stored in a reference cross section area memory 117 in advance, and they are connected to a CPU 21. The consumption coefficient Cn selected by the material specified by the consumption coefficient of the consumption coefficient file 115 and the reference cross section area A of the reference cross section area memory 117 are fed to the first arithmetic processing unit 119 respectively, the actual cut area An of the material of the work piece W cut by a sawing machine 1 is determined based on the values detected by individual sensors and fed to the first arithmetic processing unit 119, and the consumption rate (%) of a band saw edge 7 is calculated and displayed on a CRT or the like by an output device 113.