To significantly reduce a sequence of assembling steps and increase durability by activating a cam mechanism through the relative rotary action of a front shaft and a rear shaft and further, arranging a knock push bar which activates a mechanical unit to the rear shaft by causing the knock push bar to penetrate the cam mechanism.

A head crown stopper 4 rotates following the rotation of a rear shaft 3 to the right, and at the same time, a rotor 7 rotates and in turn, a cam face 8 pushes the protrusion 10 of a sliding element 9 forward. As the protrusion 10 of the sliding element 9 is prevented from rotating by a groove 11 in a cam cylinder 2, the sliding element 9 only moves forward without rotating and at the same time, pushes the rear end of an outer pipe 17 for a mechanical unit. Consequently, this pushing action enables the forward movement of the mechanical unit and the ensuing protrusion of a mouthpiece 20 from the tip metal 21 of a front shaft 1. In this case, the protrusion 10 of the sliding element 9 fits into a recessed part at the tip of the cam face 8 to hold the sliding element 9 in such a state. Further, the stepped part 14 of a knock push bar 12 is pulled to move forward together with the sliding element 9 as the stepped part 14 of the knock push bar 12 is engaged with the stepped part 15 of the sliding element 9.