PURPOSE: To display several previous shots before a defective shot instantly, and also display shots in the past going back by means of display of several shots at a time successively for analysis when the trouble is not clarified by one display.

CONSTITUTION: Actual data is measured by an actual data collecting unit 15, and the data is transferred to a defective product distinguishing unit 16 and an actual data tentative storing unit 17. Several tens of past shots of actual data received by the tentative storing unit 17 are stored therein. The defective product distinguishing unit 16 compares the received actual data with the set value (b) transferred from a setting device 13 preliminarily to distinguish whether it is a good product or not. When the same is defective, data transfer signals (e) is issued to the actual data tentative storing unit 17 and a storing unit 18. When the actual data tentative storing unit 17 receives the data transfer signal (e), several shots of actual data stored in the past are transferred to the storing unit 18. Thus, the several shots in the past before the defective shot can be displayed on a display 14 by the operation of the setting device 13.