To provide a braiding composition base composed of a thin and uniform braiding layer obtained by closely braiding a broad ribbon yarn (prepreg slit yarn) on a mandrel without leaving spaces.

The braiding composition base made of a broad yarn is produced by preparing a pair of braids 11, 12 having a braiding angle of ±θ° based on the axis of the mandrel by a broad ribbon yarn WY, braiding the broad yarn around the mandrel without leaving spaces in the direction of width to form a cylindrical braiding layer 15 and opening the braiding layer by cutting the cylinder along the axial direction of the mandrel.