To provide an activating device for fuel capable of suitably and easily reducing consumption of fuel by improving combustion efficiency of fuel.

Ore balls 28 formed by drying are filled in an interior of a container body 4 provided with a fuel inlet 5 and a fuel outlet 7 to circulate fuel, and it is composed so as to contact the fuel to the ore balls 28. By this, the fuel is activated, the combustion efficiency of the fuel is improved, and the consumption of the fuel can be suitably and easily reduced.