The present invention provides a hot water storage-type boiler having both a heat amount proportional control function and a backflow prevention function to prevent a backflow of exhaust gas with a simple structure. In the present invention, since a check valve is integrally coupled to a burner duct, there is an effect of convenient assembly. In addition, since the check valve is built in the burner duct, the check valve does not protrude to the outside, thereby having an effect that a separate space is not required.