PURPOSE: To detect overwork of a press machine, by comparing the quantity of work derived by use of the maximum detected load in case of pressing by a press machine, and the maximum stroke, with the quantity of allowable maximum work set in advance.

CONSTITUTION: When molding vessels A, B shown in the figure by a press, a press load is varied in each state shown in the figure, and the work quantity of the press is obtained by integrating said press load by a press stroke of a press machine. As a result, its estimated value W the maximum load × the press stroke × a corrected value is obtained. Subsequently, the operation for deriving this work quantity is executed at every pressing process, and each work quantity is integrated. Subsequently, this integrated work quantity is compared with the quantity of allowable maximum integrated work set in advance, and an excess of said integrated work quantity is detected. According to this method, a safe operation of a press machine, and a life control of a metallic mold, etc. can be secured.