PURPOSE: To perform proper correction of processing in a rapid displacement state during the start-up of a device by deciding a correction amount through computation of an increase amount of a tolerance based on a detecting result by a detecting means during a period between the start-up and stabilization of the device, and correcting operation of a processing part.

CONSTITUTION: The size of a work conveyed to a work carriage conveyor 4 is accurately measured by a measuring device 6. The tolerance of a work obtained at processing at two times before a current processing is stored in a first measurement memory M1 and the tolerance of a work obtained at preceding processing in a second measurement graduation M2. When the actual number (n) of operating times does not attain the number N of operating times required for bringing of a processing device into a stabilizing state, a correction value is determined from the values of the measurement memories M1 and M2 responding to tolerances A at two times before and a preceding tolerance B, and processing is carried out by using the correction value.