A distance measuring device according to an embodiment includes a first device including a first transceiver configured to transmit a first known signal and a second known signal and receive a third known signal corresponding to the first known signal and a fourth known signal corresponding to the second known signal, a second device including a second transceiver configured to transmit the third known signal and the fourth known signal and receive the first and second known signals and a calculating section configured to calculate a distance between the first device and the second device on a basis of phases of the first to fourth known signals, and the first transceiver and the second transceiver transmit/receive the first and third known signals one time each and transmit/receive the second and fourth known signals one time each, performing transmission/reception a total of four times.