Abstract: A measuring apparatus which makes use of spatio-temporal derivative method has a sensor which may be a pair of cameras for picking up images of a three-dimensional object, computing unit for processing the signals by applying spatio-temporal derivative method to the signals representing the images so as to determine physical amounts of the object such as heights of different regions on an object and self-estimation values such as values indicative of validity of the height data, judging unit for judging the validity of the physical amounts determined by the computing means on the basis of the self-estimation values, and control unit for varying, when there is any physical amount having low validity, the measuring condition of the sensor such as the distance between the sensor and the object so as to enable the sensor to obtain the signals again, while restarting the computing means and the judging means.