[Problem] To present a small-diameter magnesium base alloy tube and its manufacturing method of long length, high dimensional precision, and excellent mechanical properties.[Solving Means] A raw material 1 of aluminum base alloy is extruded and formed by using a forming pattern comprising an upper pattern 2 having plural through-holes 21 for supplying the raw material into diaphragms of equal angles on the circumference and circular cylindrical protrusions 22 positioned in the center of plural through-holes 21 so as to be surrounded by plural through-holes 21 at the exit side of the through-holes 21, and a lower pattern 3 positioned in the concave portions commonly penetrating at the exit of the plural through-holes 21 of the upper pattern 2, having through-holes 32 for inserting the protrusions of circular circumference of the upper pattern by providing a tube forming gap, positioned in the center of concave portions 31 of the concave portions 31 in the circular columnar shape of the upper pattern 2.
