PURPOSE: To reliably discharge exhaust gas to the outside of a room at an operating time, by closing a switch which enables operation of a heating device under a condition that the door of a window is opened in an appropriate state.

CONSTITUTION: An outdoor suction exhaust system combustion heating device 1 is mounted to a window frame 12 of a window 8, having a sliding type door 9, through a fixing frame 11, and open ends 6' and 7' of a suction pipe and an exhaust pipe are caused to emerge from the back and are positioned at an indoor side from a sliding sill of the door 9. A lead switch 14 is attached to a support pipe 11b of the fixing frame 11, and a permanent magnet 16 is installed to one side end of the door 9 to actuate the lead switch 14. The lead switch 14 is connected to series to a coil 19 for making and breaking a safety switch 18 located between a control circuit 16 for a heating device and a power source 17. When the door 9 is positioned in a condition shown in a second drawing which permits the connection of the open ends 6' and 7' of the suction pipe and exhaust pipe to the outside of a room the safety switch 18 turns ON to enable the operation of the heating device 1.