PURPOSE: To detect an abnormal load value and to prevent failure of dies in the stage of pressing with a press machine by measuring press load at every prescribed change in the stroke of a pressurizing mechanism and comparing the same with the preset normal load value.

CONSTITUTION: In the stage of pressing a metallic blank material to an intended shape by means of dies with a pressurizing mechanism constituted of a rod which is moved upward and downward by the rotation of the crank shaft of a press machine, the press load of the pressurizing mechanism is measured at every prescribed change in the stroke of said mechanism. The measured value and the preset value changing with each stroke is compared and when it is detected that the measured value is an abnormal value larger than the set value, the driving of the press machine is stopped automatically, whereby the accelerated wear of the dies owing to exertion of abnormal load thereupon and the reduction in the service life of the dies are prevented.