When measurement is conducted using a measurement system utilizing a tracking-type laser interferometer, laser light is emitted at a retroreflector, the tracking-type laser interferometer is placed in a tracking state, and a displacement body is displaced to a desired point and a combination of position data of the displacement body at a single desired location and rotation position data of a biaxial rotation mechanism from the tracking-type laser interferometer is stored. When a received light determiner determines that there is an abnormality in an amount of light, the positions of the displacement body and the biaxial rotation mechanism are maintained, and the displacement body and biaxial rotation mechanism are displaced to the respective stored, predetermined positions. When the abnormality in the amount of received light is eliminated after displacement, the tracking-type laser interferometer is placed in the tracking state and measurement is restarted.