PURPOSE: To obtain a modified cross-section fiber having stable shape of cross- section by performing melt spinning of polypropylene, etc., using a cap for spinning of the modified cross-section fiber installing a pyramidal protruding part on spinning face surrounded with spinning solution-dividing and ejecting holes having the modified cross-section and further providing grooves at a specific position in the protruding part.

CONSTITUTION: Spinning solution such as polypropylene is subjected to melt spinning using the subject cap for spinning of a modified cross-section fiber. The cap has solution-dividing and ejecting holes 1' having a modified cross-section and plurally divided at the center of the modified shape, pyramidal protruding part 4 on spinning face of central part surrounded with the said solution- dividing and ejecting holes 1' and further grooves such as V letter-shaped groove 5 at the side of the said spinning solution-dividing and ejecting holes in the outer periphery of the said protruding part 4. Said spinning solution is ejected from the said spinning solution-dividing and ejecting holes and introduced into the said grooves in pyramidal protruding part at the end edge of central part side. Then the spinning solution surely flows to the central part, thus the modified cross-section fiber having stable shape of cross-section is obtained.