[Problem] To provide a novel metal tube adapted to be formed with an embossed inner surface by press work, and a manufacturing method therefor. [Solution] The present invention is characterized in that a forming mandrel provided with a molded protrusion group for forming embossment is inserted into the inside of a metal tube, the forming mandrel and the metal tube are relatively brought closer to each other and brought into pressure contact with each other such that the molded protrusion group is pressed against the inner surface of the tube, and the inner surface of the metal tube is embossed by the molded protrusion group. The present invention is also characterized in that when the forming mandrel is brought into pressure contact with the inner surface of the metal tube, a pressing plunger is pressed into the metal tube from a work hole previously formed on the opposite side to the pressure contact side, the forming mandrel is brought into pressure contact with the inner surface of the metal tube, and the
