An inner burr cutting, inner face cleaning and inner face painting apparatus for long pressure-welded pipes of medium and small diameters comprises a carriage mounted on a base for reciprocal movement, a supporting tube mounted on the carriage to be inserted into a long pressure-welded pipe of a small or medium diameter, a hollow rotary shaft projecting from the supporting tube, an inner burr cutting device fixed to the rotary shaft, a mechanism for centering the inner burr cutting device in the pressure-welded pipe, a spatter crushing brush, an electromagnet device for attracting spatters and inner burr chips, a spattering prevention device, a paint spraying device disposed ahead of the electromagnet device, and a cooling device surrounding the pressure-welded pipe. After the inner and outer burrs have been removed, the cooling device, spatter crushing device, electromagnet device and paint spraying device are used to clean the inner face of the pressure-welded pipe and paint the portions of the inner face of the pressure-welded pipe from which the inner burrs are removed and which are burnt.