To provide an apparatus for the extractive distillation of a conjugated diene suppressing the formation of polymers in the extractive distillation apparatus to decrease the staining in the apparatus, clogging of piping, lowering of thermal efficiency and damage to the connection part of pipes, etc.

The invention discloses (1) a method to introduce a polymerization inhibitor into a dead space in a pipe, a column or a heat-exchanger in a method for the separation and purification of a conjugated diene by the distillation of a petroleum fraction containing the conjugated diene and (2) a method to introduce a polymerization inhibitor into a dead space in a pipe, a column or a heat-exchanger in a method for the separation and purification of a conjugated diene by the extractive distillation of a petroleum fraction containing the conjugated diene followed by the separation and purification of a compound having a boiling point higher or lower than that of the conjugated diene by distillation.