Structure monitoring software includes measuring software, arithmetic software, and communication software. The measuring software collects an output signal from an inertial sensor, stores a result of collection into a first storage unit, and outputs the result of collection to the arithmetic software. The arithmetic software computes the result of collection received from the measuring software, stores a result of computation into a second storage unit, and outputs the result of computation to the communication software. The communication software stores the result of computation received from the arithmetic software into a third storage unit and transmits the result of computation to outside. Management software determines whether each of the measuring software, the arithmetic software, and the communication software is operating normally or not, and terminates and restarts the software that is not operating normally.