The present invention improves a conventional Bunsen burner by providing it with a primary combustion chamber which covers the primary flame forming portion of the Bunsen burner and which has a secondary flame hole immediately above the primary flame forming portion. The burner apparatus of the present invention produces reduced NOx since the overall combustion is divided into primary flame combustion and secondary flame combustion. Further according to the invention, an indication of incomplete combustion due to oxygen deficiency in the ambient air or blockade of the primary air passage can be dependably detected for cessation of combustion by providing a flame rod and measuring the impedance (or ion current) of the rod.