PURPOSE: To measure a three-dimensional position coordinate after the assembling of a part.

CONSTITUTION: An object 70 to be measured is arranged between a projection side optical system 15 movable in the Z axis and a receiving side optical system 21. A belt-shaped laser light 14 is made to irradiate a plurality of objects 70 to be measured containing a drum unit having a reference end face as reference of the height from different two directions to determine coordinates of two different projection positions. Then, first three-dimensional position coordinates of the plurality of objects 70 to be measured are obtained from the two different position coordinates, an angle of rotation and a moving value in the Z axis. Then, a drum unit is set at a specified position from the results of the first three-dimensional position coordinates to determine the center height of a tape from the result of measuring the reference end face and the three-dimensional position coordinates is obtained with the tape center height as reference. This enables non-contact measurement of the three-dimensional position coordinates of a part after assembled at a high accuracy and at a high speed with the reference end face of the drum unit as reference.