A tracking type laser interferometer including: a retro-reflector 20 for
reflecting incident measurement light and returning the same in the
incident direction and a main body 10 having means for emitting
measurement light, means 30 for receiving return light reflected by the
recursive reflector and returned therefrom, and means 40 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 the tracking type laser interferometer 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,
wherein at least one light reflecting means 80 is disposed in an optical
path between the main body 10 and the retro-reflector 20, and the
directions of the optical axes of the measurement light and return light
are changed, whereby without moving the tracking type laser
interferometer, the measurement range can be expanded, and the
measurement accuracy at a specific point can be improved.