2c the ribbon of fibers is withdrawn continuously from a yarn guide hole 8 formed in the central portion of a separator 7 to create spun yarns in this spinning frame the factors displacing the fibers to the sliding wall 2b of the rotor 2 are the rotary centrifugal force of the rotor 2 and the rotary stream of accompanying air current generated by the friction between the sliding wall 2b and air it has been considered that the speed of this rotary stream in the spinning chamber increases toward the sliding wall 2b from the rotational center o1 of the rotor 2 as indicated by v1 or v2 in fig3 on the other hand the results of tests using a pitot tube have confirmed that in the spinning chamber 1 as is seen from the speed distribution indicated by the solid line in fig3 wherein the ordinate represents the speed of the rotary stream while the abscissa represents the distance from the rotational center o1 of the spinning rotor a rotary stream v3 having a considerably high speed which depends upon an accompanying air current is formed in the boundary layer in close proximity to the sliding wall 2b in other regions however there is only a rotary stream v4 which is formed by the flow of air into the inner opening 3a of the exhaust vent 3 it is known that if the length of the exhaust vent 3.