The object of the present invention is to provide a gas water heater and a hot water supply device having the same, wherein the gas water heater can properly respond to a situation in which a hot water consumption is greater than a hot water generating capacity and can be compatibly used in all situations where the hot water consumption is higher or lower than the hot water generating capacity. To achieve this objective, a gas water heater of the present application includes: a direct water pipe (111) for inflow of direct water; a flow rate sensor (120) which is mounted on the direct water pipe (111) and measures the flow rate of the direct water; a heat exchanger (130) which carries out heat exchange of the direct water, which passes through the flow rate sensor (120), by the combustion of a burner; a hot water pipe (112), through which hot water heated at the heat exchanger (130) flows; a flow rate control valve (140) which is mounted on the hot water pipe (112) and controls the flow rate of the hot water to be discharged; and a bypass pipe (113) which is connected to a direct water branch member (114) and the direct water pipe (111) at one side end and the direct water and hot water mixing member (115) and the hot water pipe (112) at the other side end. The gas water heater of the present application is characterized in that an opening and closing valve (150), a pump (160) and a three-way valve (170) are mounted on the bypass pipe (113), wherein the opening and closing valve (150) controls the flow of water flowing through the inside of the bypass pipe (113), the pump (160) circulates the water in the pipe, and the three-way valve (170) has an opening degree which is set to connect any two of three paths.