To provide an apparatus having a simple and strong structure for simply cleaning the interior of a C-shaped steel pipe having a slit.

A rotatory power generation part 5 comprising a cylindrical casing housing an impeller 17 is vertically provided on the upper surface of a pedestal plate 3. A pipe 11 for applying pressure water to the impeller 17 and a flow rate adjusting valve 13 are connected to the rotatory power generation part 5. The impeller 17 is connected to a brush part 7 suspended from the undersurface of the pedestal plate 3 and the brush part 7 having bristles provided to the periphery thereof is rotated by the rotation of the impeller 17. A circular port 39 is provided to one end of the pedestal plate 3 and a discharge port 37 is also provided to the side surface of the rotatory power generation part 5. The water discharged from the rotatory power generation part 5 is allowed to flow in an area under the pedestal plate 3 through the circular port 39 to be put to practical use as washing water.