PURPOSE: To shorten the construction term of installing a boiler and reduce work at a high place by constituting a boiler proper from an upper body and lower bodies, hanging up the upper body after assembling each body separately, placing the lower bodies under the upper body and, thereafter, combining these bodies together.

CONSTITUTION: When a boiler proper is installed, a boiler support frame body 2 is first assembled, fixed pulleys 11 are provided on beams 8 positioned at the upper end of a boiler proper accommodation portion, hanging wires 12 are led to the boiler proper accommodation portion through the fixed pulleys 11, and a hanging structure 10 is suspended by provided on a beam 8 positioned at the intermediate part in a pipeline/duct system accommodation portion 9 in such a manner that it may be free to move horizontally along a rail 14. After the upper and lower bodies 3a. 3b of the boiler proper are assembled respectively in each accommodation portion by means of the hanging structures 10, 13, the upper body 3a is lifted, and the lower bodies 3b are moved to a position under the upper body, thus the boiler proper 3 is assembled by joining the upper and lower bodies 3a, 3b together.