PURPOSE: To always produce the safe and most energy-saving condition of combustion by eliminating the defects of control on combustion due to information shortage by using a solid pickup element and a micro computer.

CONSTITUTION: A filter 15 through which visible light rays pass is provided at part of a combustion chamber 5, and a flame detector 17 using a solid pickup element 16 is attached to near the filter 15 on the outside of the combustion chamber 5. The flame detector 17 is led to an electronic controller 18 on which a micro computer is mounted, and the electronic controller 18 drives a fuel- porportional control driver 23, the primary air proportional control driver 11, and the secondary air proportional control driver 12 and is also connected with a combustion fan 10 and a hot water sensor 9. Thus, much information which could not be obtained by temperature sensors can be obtained and safe control is made possible.