Oxide of nitrogen (NOx) is one of the harmful air polluting substances generated in fuel combustion in boilers. This paper introduces the results of the basic tests conducted to clarify the NOx emission characteristics of the pulverized coal flame using reactor tubes, and the similarity in NOx emission of coal burners the concept of the low NOx burner based on the above studies, together with the results of the combustion tests of the test burners, is also described.