To provide an extruding die for forming a flat multi-hole tube in which the failure of forming the holes and shortage of strength are hardly generated.

Two lines of projecting part trains in which a plurality of projecting parts 2...2, 3...3 are lined up at intervals are provided and a part of a wall surface is formed with planar wall surfaces 2a, 3a or flat curved walls which are opposed to each other between adjacent projecting parts 2, 3 in different lines. It is desirable that the planar wall surfaces 2a, 3a or the flat curved walls are opposed to each other in nearly parallel between the adjacent projecting parts in the different lines and, further, it is desirable that an extended line in the width direction is not situated inside the tangents 5, 6 of the other projecting parts. By using the extruding die, the flat multi-hole tube which is excellent in formability and has few defects when manufactured by the extrusion can be manufactured.