PURPOSE: To improve reliability in performance, by including such a condition that the count of a counter reaches the desired value in the condition required to reset the counter.

CONSTITUTION: According as a pulse 6a is produced out of a pulse generator 6 with a crop shear 1 driven by a drive unit 3, the count of a counter 7 progresses whereby a pulse generator 10 produces a signal 10a. In the duration of the signal 10a still alive, if a signal 5a of a censor 5 is generated, an AND gate 11 opens and thereby a signal 11a is outputted. While the signal 10a is ungenerated, even if the censor 5 gives forth the signal 5a, the AND gate 11 will not open. In this controller, it is so designed that a period of resetting the counter is determined according to the contents thereof and yet the counter can be reset to only the senor's pulse produced in this period, so that reliability can be improved.