PURPOSE: To simplify the mechanism and to obtain simple and secure operation of a soot blower by a method wherein the operation of an outer tube is carried out by a cylinder mechanism.

CONSTITUTION: A command to start soot blow is transmitted to respective timer 42, 37 and 32 from a control box 52, then a valve 19 first opens, thereby starting an injection of such as stream which is a medium for the soot blow through an inner tube 21 and outer tube 4 and out of a nozzle 4a. On the other hand, receiving a command from the timer 32, a motor 1 starts operating to rotate the outer tube 4 through a key 5 by small and large gears 2 and 3. In the outer tube 4, a key groove is engraved by the length corresponding to a stroke length. The outer tube is supplied with pressurized gas from a tube 53 via a member 44b, therefore a piston comprising the outer tube 4 and a piston head 41a is made to advance, and rotate by receiving a rotating force which is transmitted by the key 5. Accordingly, the nozzle 4a draws a spiral locus.