Patent ID: 7583374

Claim:
A measurement method using a tracking type laser interferometer that includes: a recursive reflector for reflecting incident measurement light and returning the same in the incident direction and a main body having means for emitting measurement light, means for receiving return light reflected by the recursive reflector and returned therefrom, and means for controlling the emission direction of measurement light so that the distance between both optical axes of measurement light and return light becomes constant at all times, and outputs a measurement value in response to an increase or a decrease in distance between the reference point in the main body and the recursive reflector, the method comprising the steps of: disposing at least one light reflecting means in an optical path between the main body and recursive reflector; and changing the directions of the optical axes of measurement light and return light, wherein measurement is carried out by regarding a virtual image position of the reference point, which is formed by disposition of the light reflecting means, as the reference point.