PURPOSE: To carry out adjustment according to the change in a state of a main spindle chuck being used, such as the change between a state of outer diametral chucking and inner diametral chucking, only by carrying out simple operation.

CONSTITUTION: Position detection switches LS1-LS3 for detecting the expanded/ contracted position of a chuck cylinder 10 that opens/closes a main spindle chuck 6 are provided on a identifying device 13 for open/close state of the main spindle chuck 6. An open/close state detection means 13 for detecting the open/close state of the main spindle chuck 6 based on the ON/OFF state of the position detection switches LS1-LS3, is provided. Certain types of open/ close judgement references 13a-13f are provided on the open/close state detection means 13. A judgement reference alterlation means 14 for selecting the open/ close judgement references 13a-13f corresponding to a set data, is also provided.