Abstract: An aircraft health diagnostic device is provided with a control unit that carries out structural health monitoring of a structure of an aircraft. The control unit has a first risk assessment unit that assesses the risk of damage occurring in the structure on the basis of a correlation between reference data stored in a storage unit and a signal data set based on measurement data obtained through measurement carried out by a measuring instrument, a second risk assessment unit that assesses the risk of damage occurring in the structure on the basis of the time-sequence change in the behavior of the signal data set, and a maintenance assessment unit that assesses the life, repair timing, and a maintenance plan of the structure on the basis of the time-sequence change in the behavior of the signal data set.