In a case in which three or more movable objects, each of those detecting the relative position with respect to another movable object, are able to communicate with each other: a reference movable object obtains observation data and transmits the observation data to non-reference movable objects; one non-reference movable object calculates the relative position with respect to the reference movable object by performing interferometric positioning using the observation data obtained by the observation data obtaining means and data including observation data received from the reference movable object, and also transmits data including an integer bias calculated as interferometric positioning results to another non-reference movable object and receives reliability determination results regarding the interferometric positioning; and the another non-reference movable object receives data including the integer bias from the one non-reference movable object and determines the reliability of the interferometric positioning.