To provide a biomass fuel water heater capable of remarkably reducing the generation of smoke caused by the incomplete combustion of biomass fuel, and controlling hot water with high accuracy.

This biomass fuel water heater 1 comprises a fuel tank 2 storing biomass fuel such as grain, sawdust, wood pellet and the like, a combustion portion 3 for burning the biomass fuel, a fuel supply device 4 supplying the biomass fuel from the fuel tank 2 to the combustion portion 3, a hot water tank 7 comprising water temperature sensors 5, 6, and a heat exchanging portion 8 between the combustion portion 3 and the hot water tank 7. A burner combustion device 14 by fluid fuel such as kerosene, gas and the like is also disposed in a combustion chamber 10 of the combustion portion 3. One or both of the biomass fuel and the fluid fuel supplied from the fuel tank 2 are burnt.