A method for measuring ash content of food stuff is carried out by 1) preparing, with respect to food stuff samples whose ash content values are known, a calibration curve by a non-linear analysis of absorbance values and the known ash content of each sample, the absorbance values being obtained by irradiating light having particular wavelengths containing at least an ultraviolet ray band wavelength, the particular wavelength being specific to organic ingredients well coupled to inorganic ingredients which result in the ash content, and 2) deriving, with respect to a sample whose ash content value is unknown, an ash content value of the sample from absorbance values obtained by irradiating, on the sample, light having the particular wavelengths containing at least the ultraviolet ray band wavelength and from the calibration curve prepared in advance by the non-linear analysis. An apparatus for carrying out the method includes a light source section, a photo detecting section, a storing section for storing the calibration curve, and a calculation section for calculating, with respect to a sample whose ash content value is unknown, the ash content value based on the absorbance values and the calibration curve stored in the storing section. It is possible to speed up the measuring operation and to improve the measuring precision.