Mirror replacement device for a segmented mirror telescope and mirror replacement method thereof

A mirror replacement device includes a gripping mechanism to grip a segment mirror, a fine drive mechanism to change a position and a posture of the gripping mechanism, a lift mechanism for the segment mirror, a first detector to detect a relative position and a relative posture between a comparison object and a target object, a second detector to detect a bend of the fine drive mechanism, and a mirror replacement controller to replace the segment mirror based on detection signals output from the above-mentioned detectors. The controller determines whether the first detector can successfully perform a measurement. When it is determined that the measurement can be successfully performed, the control is performed based on the detection signal output from the first detector. When it is determined that the measurement cannot be successfully performed, the control is performed based on the detection signal output from the second detector.