PURPOSE: To compactly constitute a boiler apparatus reduce NOx and increase heat exchange area by installing a ceiling burner on the ceiling wall of a boiler main body, forming a combustion chamber 3 in space right under the ceiling burner 2 and arranging a group of water pipes to the side part of the combustion chamber.

CONSTITUTION: A ceiling burner 2 is installed on the ceiling wall of a boiler main body, a combustion chamber 3 is formed in space right under the ceiling burner 2 and a group of water pipes 4 are arranged to side part of the combustion chamber 3. Part of the water pipes 4 have bent part 5 bent toward the inside of the combustion chamber 3. Temperature of the combustion chamber 3 is controlled at around 1300°C by the group of the pipes 4 having the bent part 5. Combustion gas generated by the ceiling burner 2 continues burning in the interior of the combustion chamber 3 and simultaneously effects heat exchange with the group of the water pipes 4 before being exhausted. In the interior of the combustion chamber 3, therefor, oxidation of CO is actively effected and so-called thermal No and the like are prevented from being generated so that the generation of NOx is suppressed. The boiler apparatus can be compactly constituted.