A melt-processable fluorine-containing polymer is melt kneaded with a
kneader which has a residence time of at least 10 minutes, a usable volume
ratio (usable space in a container/space in a container) of larger than
0.3, and a power factor K of less than 8000, the power factor K being
represented by the formula: K=Pv/.mu./n.sup.2 in which Pv is a power
requirement per unit volume (W/m.sup.3), .mu. is a melt viscosity (Pa.s),
and n is a rotation speed (rps), to effectively remove terminal groups and
bonds in the backbones, which are unstable during melt kneading, from the
melt-processable fluorine-containing polymer, and obtain a colorless
fluorine-containing polymer.
