To provide a fuel modification tool by magnetic force and far infrared irradiation and its production method.

A fuel modification tool and its production method utilize an expanded resin obtained by mixing a ceramic, a carbon powder, a radioactive rare earth ore, and a magnet with a synthetic resin and expanding the resulting mixture. As the synthetic resin, a urethane resin, a polyester resin and the like are used, and an expanded resin obtained by mixing a mixture of a plurality of different ceramic powders and a carbon powder with the resin and expanding the resulting mixture is joined with an expanded resin obtained by mixing only a ceramic powder with the resin and expanding the resulting mixture and put in use. The fuel modifying tool and its production method comprise a mixed product 10 obtained by mixing a ceramic powder, a carbon powder, a radioactive rare earth ore powder in a synthetic resin which is joined with an expanded resin 11 obtained by mixing only a ceramic powder with the resin and expanding the resulting mixture and further, a magnet 12 encapsulated therein in a housed form.