Does color confinement imply massive gluons?

Color confinement is one of the central issues in QCD, and there are various interpretations of this feature. In this paper we have adopted the interpretation that colored particles cannot be observed just because colored states are unphysical in the sense of Q_B|quark〉≠0, Q_B|gluon〉≠0. It is shown that there are two phases in QCD distinguished by different choices of the gauge parameter. In one phase, called the “confinement phase,” color confinement is realized and gluons are no longer massless. In the other phase, called the “deconfinement phase,” color confinement is not realized, but the gluons remain massless.