To obtain combustible chaff changed so as to be combustible in order to effectively utilize chaff having water repelling property and being industrial waste-like material of rice bowl because of slow flammability and produce chaff fuel having good combustion efficiency as further rational use.

Melted wax is mixed with chaff to assimilate the wax with cuticular layer covering epidermis of chaff. As a result, solid membrane of wax-like substance of the cuticular layer gradually comes in close to a gas membrane and the surface tension is changed. Continuous film of the wax-like substance of the cuticular layer produces numerous pores by being affected by two-dimensional saturated vapor pressure generated in this time. The pores produced in the film play role of a vent hole. Further, melted wax, etc., are absorbed into chaff and when the chaff is burned, the chaff is burned as combustion medium and combustion efficiency is enhanced by synergistically making the wax act on combustion of chaff. The combustible chaff can be formed into rational chaff fuel. The chaff fuel burns without being inhibited by characteristics which chaff has.