PURPOSE: To carry out stable fuel activating treatment with a small amount of activator so as to miniaturize a fossil fuel activating apparatus and reduce the weight thereof, by forming a container main body storing in its inside, activator having oxide of rare earth group element as effective component, in nearly an U-shape pipe shape.

CONSTITUTION: Fuel which is supplied from a fuel tank 2 and flows from the flow inlet 1a of a container main body 1 is passed through a space 6, and it flows in an activator storing part 8 storing activator 9 having rare earth group element oxide as effective component, and then it passes a space 7 and supplied from a discharging port 1b into an engine 3. At this time, when flowing fuel passes a perpendicular parts 1c, 1d, it passes while being brought in contact with the activator 9 evenly and uniformly by action of gravitation, and activating treatment is carried out. In the spaces 6, 7, vortex of fuel generated at the time of passing the space of the activator 9 is damped temporally, and the deviation of pressure is eliminated. It is thus possible to prevent generation of turbulence flow, smooth flow of fuel, and also prevent generation of bubbles.