PURPOSE: To exchange heads smoothly by providing a holding device to hold a head to be exchanged by lifting it to the upper side, to one end side in the lateral direction of a saddle.

CONSTITUTION: Upper male cones 35a and 35a, and a lower female cone 35b are positioned opposite to the upper female cones 41 and 41 of a head saddle 15a and a lower male cone 44. Then, by operating a clamp cylinder 45 to extend, the lower male cone 44 is moved to the upper side, and engaged with the lower female cone 35b of the first exchanged head 17a from the lower side. At the same time, the first exchanged head 17a is lifted up, and its upper male cones 35a are engaged with the upper female cones 41 of the head saddle 15a. Consequently, the first exchanged head 17a is held to the saddle 15a, while a limit switch 50 is operated to confirm the above holding.