To increase the number of measurement repetitions and measurement accuracy in a gravity gradient meter.

Objects equivalent to the two mirrors of a Michelson interferometer are separately allowed to fall freely, and a temporal change in the displacement therebetween is measured by the output of the interferometer. A first free-falling object 1 provided with a first reflecting mirror 4A and a beam splitter 5 and a second free-falling object 2 provided with a second reflecting mirror 4B are allowed to fall freely. A piezoelectric element 160 is used as a release mechanism for the free-falling objects 1, 2. The gravity gradient measuring apparatus is provided with first support mechanisms 12, 13 constituting a falling mechanism and a returning mechanism and second support mechanisms 14, 15.