A spray coating tool used for coating the inner surface of a tube. The tool sprays a desired paint through a nozzle while the tool is being shifted inside the tube to be coated along the axis of the same tube. In the nozzle a nozzle insert having a prism portion, on the external surface of which at least one spiral groove is formed, is inscribed to the inner surface of a hollow cylindrical space of a nozzle cap of the above-mentioned nozzle. A plurality of straightly elongated grooves, formed between the inner surface of the nozzle cap and the sides of the prism portion of the nozzle insert, and the spiral groove function to impart atomizing gas a straightly going force and a spirally going force, so as to spirally spray the paint supplied through a paint supply passage extending along the axis of the nozzle insert.