Abstract: An ultrasonic flaw detector driving apparatus with no guide rail and including a traveling member (2) capable of being freely mounted to and dismounted from piping (1) to be inspected, and a turning member (3) detachably attached to the traveling member for turning movement thereabout. The traveling member is equipped with a multiplicity of sets of traveling rolling elements (9,9a) maintained in contact with an outer peripheral surface of the piping and spaced apart from one another circumferentially of the piping while each set of the traveling rolling elements of comprises at least two rolling elements which are spaced apart from each other axially of the traveling member (2). The turning member (3) is equipped with at least one ultrasonic wave probe (4) which scans the outer peripheral surface of the piping to inspect it.