PURPOSE: To automate and simplify tool change and to increase the efficiency by operating each operating means such as an operating means for a muffler seaming member or an operating means for a moving base at a suitable timing.

CONSTITUTION: Each muffler seaming device 24 is advanced, a tool supporting base is moved toward the device 24 and an adapter 56 for the tool 58 is fitted into a fitting hole. A cylinder 51 is operated to close a collet chuck 48, the tool 58 is fixed to the side of the muffler seaming device 24 and the tool supporting base is lowered to remove the engagement with tool 58. Then, 1st and 2nd cylinders are operated to move the moving base as far as a tool stand by position to return a rocking axis 70, a rocking bracket 80, a seaming arm 22 and a cam follower 20 is fitted from the front into a cam groove 18 to be put in a usable state. In this way, tool 58 change can be performed automati cally and easily.