A displacement detecting device for a structural object (69, 90, 91, 92, or 93) comprising: a first attitude data calculator disposed with first two antennas (112A and 112B) at a first position of the structural object (69, 90, 91, 92, or 93), configured to calculate a first base line vector between the first two antennas (112A and 112B) by using received positioning signals, configured to calculate first attitude data of the first position based on an angle formed by three perpendicular axes in an absolute coordinate system and the first base line vector, and configured to calculate a calculated time point of the first attitude data of the first position based on a time of a positioning system; a second attitude data calculator disposed with second two antennas (212A and 212B) at a second position of the structural object (69, 90, 91, 92, or 93), configured to calculate a second base line vector between the second two antennas (212A and 212B) by using received positioning signals, configured to calculate second attitude data of the second position based on an angle formed by the three perpendicular axes in an absolute coordinate system and the second base line vector, and configured to calculate a calculated time point of the second attitude data of the second position based on the time of the positioning system; a data extractor configured to extract the first and second attitude data calculated at the same time point, based on the time of the positioning system; and a displacement calculator configured to calculate a displacement amount and a displacement direction of the structural object (69, 90, 91, 92, or 93) by using a difference between the first and second attitude data calculated at the same time point. a first attitude data calculator disposed with first two antennas (112A and 112B) at a first position of the structural object (69, 90, 91, 92, or 93), configured to calculate a first base line vector between the first two antennas (112A and 112B) by using received positioning signals, configured to calculate first attitude data of the first position based on an angle formed by three perpendicular axes in an absolute coordinate system and the first base line vector, and configured to calculate a calculated time point of the first attitude data of the first position based on a time of a positioning system; a second attitude data calculator disposed with second two antennas (212A and 212B) at a second position of the structural object (69, 90, 91, 92, or 93), configured to calculate a second base line vector between the second two antennas (212A and 212B) by using received positioning signals, configured to calculate second attitude data of the second position based on an angle formed by the three perpendicular axes in an absolute coordinate system and the second base line vector, and configured to calculate a calculated time point of the second attitude data of the second position based on the time of the positioning system; a data extractor configured to extract the first and second attitude data calculated at the same time point, based on the time of the positioning system; and a displacement calculator configured to calculate a displacement amount and a displacement direction of the structural object (69, 90, 91, 92, or 93) by using a difference between the first and second attitude data calculated at the same time point.