A device for working the interior of pipes, with an outer casing, an inner casing which is axially displaceable therein, with a rotary head which carries a bracket for attaching a working apparatus, with respective gearing arrangements each actuated by a motor, one for rotating the rotary head and another for the axial motion of the inner casing, with media-bearing ducts and control and energy supply leads introduced into the outer casing, has the following particulars: The gearing arrangement for the axial motion of the inner casing, the motor actuating this gearing arrangement, the gearing arrangement for executing the rotation of the rotary head, as well as the motor actuating this gearing arrangement, form four subassemblies which can be preassembled separately from one another. A fifth preassemblable subassembly has facilities for forming interfaces for the passage of lines from the inner casing to the rotary head. All subassemblies are accommodated in the inner casing and can be braced therein by mounting plates.