To solve the problem that in a conventional objective measuring apparatus which measures the shape of an object to be measured by using an optical cutting method, the center position of the image of slit light is deviated from the center position in the width direction of intrinsic slit light, when the object to be measured has a curved surface, such as a circular cylinder, since the center position of the image of the slit light is found by performing a load-averaging operation along the arrangement direction of image sensors used to image an optical cutting image, and that the measurement accuracy of the shape is lowered.

Since the width direction of local slit light is found along the found width direction of the slit light, and load-averaging operation is performed, the center position of the slit light is decided. As a result, the shape can be measured with high accuracy, irrespective of the shape of the object to be measured.