To provide an open type combustion apparatus capable of promptly stopping combustion of a burner when the burner is ignited with an exhaust passage closed.

The open type combustion apparatus includes a combustion prohibition means 32. After first predetermined time determined by estimating rise time of composite electromotive force of a first thermocouple 9 and a second thermocouple 10 passes after ignition of the gas burner 3 by an ignition electrode 6, until second predetermined time determined by estimating time until combustion of the gas burner 3 is stabilized after passage of the first predetermined time passes, when the state where the composite electromotive force becomes determination electromotive force or less is continued for first stabilization time or longer, the combustion prohibition means 32 closes a gas main cock 24 to extinguish the gas burner 3. After the second predetermined time passes, when the state where the composite electromotive force becomes the determination electromotive force or less is continued for second stabilization time or longer which is set shorter than the first stabilization time, the combustion prohibition means 32 closes the gas main cock 24 to stop the combustion of the gas burner 3.