It is an object of the present invention to provide a mandrel bar cleaning facility capable of effectively suppressing carburization generated on the inner surface of a pipe or tube while the pipe or tube is elongated and rolled without hindering an operation.A mandrel bar cleaning facility 15 of the present invention cleans a mandrel bar B which is pulled out of a mandrel bar conveying line after being used for elongating and rolling a pipe or tube in a mandrel mill 8. The mandrel bar cleaning facility 15 is provided with conveying devices 17, 18 that convey the mandrel bar B in the axial direction while revolving the mandrel bar B in the peripheral direction, and cleaning devices 1d that are arranged oppositely to the side of the mandrel bar B conveyed by the conveying devices 17, 18, and jet high-pressure water having a water pressure of 0.2 to 150 MPa (preferably, 20 to 150 MPa) toward the outer surface of the mandrel bar B.