PURPOSE: To enable a gun barrel to tilt and move straightly during a turning action and to reduce its size, by transmitting the change in shape of tilting cum formed on the inner surface of a circumference concentric to a turning central axis through a sliding contactor to an inclined movement lever when turning the gun barrel.

CONSTITUTION: The mud gun turns about 150° around turning center 17 from shelter position G to a press position. Over an initial interval GI, gun barrel 1 turns with a horizontal posture, and thereafter, it commences tilting movement, which is controlled by the shape of tilting cum 11 fixed to a supporting rest. Tilting lever 10 presses always sliding contactor 12 to cum 11 owing to the weight of gun barrel 1. The radius of cum 11 grows from R0 to R1 when turning further about 10° from position 1, and as sliding contactor 12 moves in the direction of arrow mark K, lever 10 also turns, gun barrel 1 being moved as tilted. Further, from immediately before to after the tilting movement is completed (over an interval MN), a straight movement mechanism furnished moves gun barrel 1 straight toward a tap hole F.