PURPOSE: To detect whether a die is inserted or not and to easily and surely discriminate whether it is mounted normally or abnormally by providing a dog at one of the die or a station, providing a sensor to detect the dog at the other and detecting a fitting angle of the die from the position of the detected dog.

CONSTITUTION: Upper and lower dies are provided with many die mounting stations S(IJ). The die is indexed directly under a ram 6 to perform a prescribed pressing to a working W guided between both turrets 3, 4. The dog Mg is provided on one of the die or the station and the sensor Se to detect this dog is provided on the other. Since a detecting circuit to detect a fitting angle of the die to the station is provided from the position of the dog to the reference position round the dog detected by this sensor, the fitting angle of the die can be detected from the detected position of the dog. In this way, since whether the die is inserted or not can be detected at the same time, whether it is mounted normally or abnormally is discriminated easily and surely, and the working efficiency can be improved and a defective product and breakage of the die can be prevented from generating.