PURPOSE: To obtain an opened staple cotton state wherein the fiber material is perfectly homogenized and mixed and wherein the irregularity of weight is little, by treating staple cotton opened and mixed in two line opening zones I in one line.

CONSTITUTION: This apparatus is provided with two or more adjacent vertical type staple fiber-feeding chambers 1, 1', and staple cotton carried through a duct 4 with a negative pressure is alternately fed into the chambers 1, 1' through a conveyer 2 and cylinders 3 which are rotated in the mutually opposite directions. A pair of cylinders or rollers 7 which are rotated on horizontal axes and used for gripping the staple cotton are disposed in the bottom portions of the chambers, respectively. The cylinders or rollers 7 are cooperated with a pair of cylinders 10 for opening cotton. Carding plates 10 are disposed at places close to the cylinders 8 for opening staple cotton. Thus, the staple cotton opened and mixed in the two line cotton-opening zone is treated in one line, thereby improving the mixing and preventing the irregularity of the weight.