To provide a number of revolution for motor detecting device for a space heating device to be capable of reading the presence of combustion and the number of revolutions of a motor by using a sensor for detecting combustion and be simple and low cost.

An optical type sensor 60 for detection of ignition, extinction of flame, and flame failure is mounted on a motor housing 22 positioned on a side opposite to a combustion chamber 14 of a combustion cylinder 16 with a blower 28 for feeding air positioned at a center therebetween. A through-hole 64 is formed in the blower 28 for feeding air and at a position, where the optical type sensor 60 and the internal part of the combustion chamber 14 are intercoupled. This constitution introduces flame intermittently to the optical type sensor 60 via the through-hole 64 of the blower 28 for feeding air, when flame light is generated in the combustion chamber 14. Namely, the optical type sensor 60 works to detect ignition, extinction of flame, and flame failure in the combustion chamber 14 and works to output the number of revolutions of the motor 24 as a pulse signal to a control circuit 30. This constitution eliminates sensors which were needed heretofore, to detect the number of revolutions of the motor 24 and reduces the cost and size.