PURPOSE: To measure accurately the weight of a lump object by using the transmission dose of X-rays which are utilized for attaining various external appearance information of the lump object.

CONSTITUTION: A lump object 4 is moved relatively to a pair of an X-ray generating source 1 and an X-ray linear sensor 5 which are arranged to face each other. X-rays from the generating source 1 are detected by a detector of the sensor 5. On a basis of the result of comparison between this detected value and a threshold, external appearance information of the lump object 4 is obtained. On a basis of all output data corresponding to the existence position of the lump object 4 in detection of external appearance information, namely, output signals smaller than the threshold out of all output signals, a transmission does I of the lump object 4 is obtained by integral values of individual transmission doses. The weight of the lump object 4 is obtained in accordance with a formula. In this formula, C is a transmission constant, and I0 is the transmission dose in case of the absence of the lump object 4.