To provide a method for preparation if a fuel which processes wasted disposable diapers, wasted plastic, bean-cued refuse and wasted food including containers such as boxed lunches and side dishes out of the shelf time and the like to obtain a fuel not emitting a harmful gas.

This fuel preparation method consists of a wasted disposable diaper introduction process in which wasted disposable diapers are introduced into a vegetable oil heated in the vegetable oil heating process for heating the vegetable oil in a pot up to 110°C-180°C, a heating and kneading process in which the introduced material is taken out after contained water is evaporated and the introduced material is softened and melted in the previous disposable diaper introduction process, a catalyst is added to this melted introduced- material and the mixture is heated and kneaded at 220°C-350°C while hydrogen chloride gas is neutralized and removed as calcium chloride, a liquefying process in which a wasted oil of vegetable oil or mineral oil is added to the mixture from the previous heating and kneading process and the mixture is heated up to 200°C-350°C it, and the fuel processing process in which the liquid from the liquefying process is processed to a liquid fuel, a liquid fuel containing solid granules, a granule fuel, a gel fuel or the like.