PURPOSE: To automatically exchange a tool between a rotary spindle and a magazine by dividing a hood into two sections along its diametral line and pivotally mounting them so as to be closeable, and providing an opening means for opening and closing them.

CONSTITUTION: A opening type hood 5 is provided on a spindle head 4. The opening hood 5 is formed in a bisected structure hood 11 so as to enclose a rotary spindle, a tool holder and a cutting tool, and the hood 11 is made to communicate with a dust collector 13 through a chip discharging duct 12. A base plate 14 is stucked to the spindle head 4, and a pair of hinge shafts 15, 15 is horizontally provided in parallel on the base plate 14. Each semicircular arc-shaped divided piece of the hood 11 i.s attached to a sleeve fitted rotatably to the hinge shafts 15, 15. The bore at a tip of the hood 11 is gradually decreased toward the tip, and a connecting arm 19 is rotated by the action of a cylinder 38 to open and close the hood 11 and moreover to keep it in an opened and a closed state.