A pointing axis estimation apparatus including a laser light source for emitting a laser light, a telescope unit which the laser light enters, and an optical axis error detector for detecting a laser optical axis variation of the laser light emitted from the telescope unit , comprising: - a laser light source unit comprising the laser light source ; - a laser light source installation part that is configured to fix the light source ; and - a first inertial sensor installed on the laser light source installation part ; - a laser light source-unit attitude detector that is configured to calculate translational and rotational displacements of the laser light source installation part based on information from the first inertial sensor ; - an optical axis detection unit comprising the optical axis error detector ; - an optical axis detection system installation part that is configured to fix the optical axis error detector ; and - a second inertial sensor installed on the optical axis detection system installation part ; - an optical axis detection-unit attitude detector that is configured to calculate translational and rotational displacements of the optical axis detection system installation part based on information from the second inertial sensor ; - a pointing axis calculator that is configured to calculate a pointing axis variations of the telescope unit based on information from the optical axis error detector ; and - a pointing error estimator that is configured to calculate the true pointing error of the telescope unit by removing the pointing variations calculated by the laser light source-unit attitude detector and the pointing variations calculated by the optical axis detection-unit attitude detector from the pointing axis variations calculated by the pointing axis calculator . - a laser light source unit comprising the laser light source ; - a laser light source installation part that is configured to fix the light source ; and - a first inertial sensor installed on the laser light source installation part ; - a laser light source installation part that is configured to fix the light source ; and - a first inertial sensor installed on the laser light source installation part ; - a laser light source-unit attitude detector that is configured to calculate translational and rotational displacements of the laser light source installation part based on information from the first inertial sensor ; - an optical axis detection unit comprising the optical axis error detector ; - an optical axis detection system installation part that is configured to fix the optical axis error detector ; and - a second inertial sensor installed on the optical axis detection system installation part ; - an optical axis detection system installation part that is configured to fix the optical axis error detector ; and - a second inertial sensor installed on the optical axis detection system installation part ; - an optical axis detection-unit attitude detector that is configured to calculate translational and rotational displacements of the optical axis detection system installation part based on information from the second inertial sensor ; - a pointing axis calculator that is configured to calculate a pointing axis variations of the telescope unit based on information from the optical axis error detector ; and - a pointing error estimator that is configured to calculate the true pointing error of the telescope unit by removing the pointing variations calculated by the laser light source-unit attitude detector and the pointing variations calculated by the optical axis detection-unit attitude detector from the pointing axis variations calculated by the pointing axis calculator . <EOS>