Abstract: An apparatus and process for etching the inner surface of a pipe or tubular member includes a primary pipe adapted to be connected with a pipe or pipes whose inner surfaces are to be treated, and treating-solution supply pipes communicating, by means of electromagnetic valves, with the aforenoted primary pipe, whereby one path for a specific solution to be fed through one of the treating-solution supply pipes by means of the primary pipe into the pipe to be treated is automatically switched to another path by means of the aforenoted electromagnetic valves, without causing mixing of one solution with another. This apparatus and process therefore provides improved operational efficiency as well as a uniform surface condition and achieves accurate dimensioning for the inner surface of the pipe to be treated.