PURPOSE: To correct the dimension of a workpiece to an aimed value in a short time and observe the scattering of dimension by controlling the dimension by the correction signal which is obtaind by the multiplication of the average value of the dimension of the workpice by the factor of critical value and the alarm signal which is obtained by the comparison and selection of the dimension of the contiguous workpiece from the average value.

CONSTITUTION: The dimension of a workpiece measured in a post process controlling mechanism is input into a substraction circuit 6, and each difference from a set value is output and then added in succession. The feedback correction value which is obtained by multiplying the critical value factor in 50W100% by the average value obtained by the division by the number N of pieces in preset, and when an FF circuit 20 is set, FB (feedback) correction signal F1', e.g., 0.1μm is transmitted, and said operation is continued up to the time when FB correction value becomes 0. The output value of the circuit 6 is read by a latch circuit 8 and output according to the next input signal and input into a subtraction circuit 9, and the contiguous value which is obtained by the output of the dimension difference of the contiguous workpiece is added in succession. When the average value which is obtained by the division by N-1 in a division circuit 12 is larger than the set value, FB alarm signal F3 is sent into an inprocess mechanism, and the scattering of the dimension of the contiguous workpiece can be observed.