Abstract: The invention relates to an apparatus with a self-displacing device for its advance in the interior of a duct for remote inspection and/or treatment. The apparatus comprises a plurality of elements coupled to one another so as to make up a train, each element of which constitutes a wagon independent of the other elements and interchangeable at will, each element fulfilling a definite function and being of a length adapted for the curves to be taken, at least one of the elements constituting a displacing element and advantageously another one of the elements constituting an element for operating the displacing element. At least one element is a holding element including a holding device bearing selectively upon the internal wall of the duct, whereas the displacing element preferably is a puller-pusher element. The apparatus is supplied with electric power and with compressed-air through a cable and a compressed-air conduit, respectively.