PURPOSE: To prevent a lance pipe from bending by forming a bent part in part of a heat-exchanger tube which is in the traveling path of the lance pipe and by supporting the lance pipe by a divided supporting member which is provided in a freely rotatable manner on a horizontal part of the tube under the bent part.

CONSTITUTION: A part of a tube 12 which is in the traveling path of a lance pipe 14 as a soot blower is formed into a laterally bent part 12A so that the lance pipe 14 travels in the space 15 formed by the bending. On a horizontal part of the tube under the bent part 12A a divided supporting member 17 consisting of a plurality of divided ring-shaped pieces 17a, 17b is fitted in a freely rotatable manner so that the lance pipe 14 is supported through the interposition of the divided supporting member 17. As a result, the bending of the lance pipe can be reduced to a small flexure without using a bending- preventive member or the like additionally.