A damage detection system comprising: a physical quantity detection unit configured to detect a physical quantity of a structural object composing an aircraft during a flight of the aircraft, wherein the physical quantity includes strain amounts, vibrations or accelerations of the structural object; a flight condition changing part configured to change at least one flight condition of the aircraft to at least one specific flight condition suitable for detection of a damage of the aircraft when the physical quantity of the structural object has been detected by the physical quantity detection unit and the detected physical quantity is not large enough to determine whether the structural object has been damaged; a damage detection part configured to determine whether the damage arose in the structural object, based on the physical quantity which has been detected, from the structural object of the aircraft flying with the changed at least one specific flight condition, by the physical quantity detection unit; and a storage configured to store at least one physical quantity of the structural object related with the at least one specific flight condition of the aircraft, the stored at least one physical quantity corresponding to the at least one specific flight condition and a state where no damage exists in the structural object, wherein the flight condition changing part is adapted to change the at least one flight condition to the at least one specific flight condition stored in the storage when the physical quantity of the structural object has been detected by the physical quantity detection unit and the detected physical quantity is not large enough to determine whether the structural object has been damaged, and wherein the damage detection part is adapted to determine whether the damage arose in the structural object, based on the physical quantity which has been detected, from the structural object of the aircraft flying with the changed at least one specific flight condition, by the physical quantity detection unit and the at least one physical quantity, corresponding to the state where the no damage exists in the structural object, stored in the storage. a physical quantity detection unit configured to detect a physical quantity of a structural object composing an aircraft during a flight of the aircraft, wherein the physical quantity includes strain amounts, vibrations or accelerations of the structural object; a flight condition changing part configured to change at least one flight condition of the aircraft to at least one specific flight condition suitable for detection of a damage of the aircraft when the physical quantity of the structural object has been detected by the physical quantity detection unit and the detected physical quantity is not large enough to determine whether the structural object has been damaged; a damage detection part configured to determine whether the damage arose in the structural object, based on the physical quantity which has been detected, from the structural object of the aircraft flying with the changed at least one specific flight condition, by the physical quantity detection unit; and a storage configured to store at least one physical quantity of the structural object related with the at least one specific flight condition of the aircraft, the stored at least one physical quantity corresponding to the at least one specific flight condition and a state where no damage exists in the structural object, wherein the flight condition changing part is adapted to change the at least one flight condition to the at least one specific flight condition stored in the storage when the physical quantity of the structural object has been detected by the physical quantity detection unit and the detected physical quantity is not large enough to determine whether the structural object has been damaged, and wherein the damage detection part is adapted to determine whether the damage arose in the structural object, based on the physical quantity which has been detected, from the structural object of the aircraft flying with the changed at least one specific flight condition, by the physical quantity detection unit and the at least one physical quantity, corresponding to the state where the no damage exists in the structural object, stored in the storage.