The objective is to obtain fuel having high combustion calorie and superior handleability from a crude glycerin or a fatty acid mixture that have been discarded as industrial waste products. Disclosed is a fuel comprising a water-insolublized fatty acid substance obtained by water-insolubilizing a fatty acid that is contained in a crude glycerin or fatty acid mixtures that are produced as by-products in the process of producing a biofuel from an animal/plant-derived fat/oil. The water-insolublized fatty acid substance is preferably a water-insoluble fatty acid salt, particularly preferably a salt of a fatty acid with a divalent or trivalent metal ion.