PURPOSE: To permit sawing as efficiently as possible by a method wherein a log sending speed is changed in accordance with a cutting length, which is changed in accordance with the configuration of the log.

CONSTITUTION: The whole configuration of a log 1, such as the length of the log, the change of sectional configuration along the axial direction of the same, curvature, twisting and the like in the axial direction of the same and the like, are measured based on the outputs of sensors 21, 22, 31-34, 41-44, 51-54 whereby the measured data are inputted into an operating device 6. In the operating device 6, the planning of cutting of the log and the method of sheeting are determined by a predetermined program based on the results of measurements and, further, cutting lengths upon cutting the log based on the determined plan of cutting and method of sheeting are operated across the whole length of the log. The results of operations are inputted into a control device 7 while the control device 7 controls the driving mechanism of a sawing device 8 based on the input so that the feeding speed V of the sawing device 8 becomes the simple reducing function of the cutting length. According to this method, cutting resistance upon sawing is kept in constant substantially whereby the efficiency of sawing is improved remarkably.