A displacement detecting device for a structural object is capable of accurately measuring displacement of the structural object. The displacement detecting device includes first and second attitude data calculators, a data extractor, and a displacement calculator. The first attitude data calculator calculates attitude data at a first position by using received positioning signals, and calculates a calculated time point of the attitude data of the first position based on a time of a positioning system. The second attitude data calculator calculates attitude data at a second position by using received positioning signals, and calculates a calculated time point of the attitude data of the second position based on the time of the positioning system. The displacement calculator calculates a displacement amount and a displacement direction of the structural object by using a difference between the attitude data of the first and second positions calculated at the same time point.