The invention provides a production process of a poly(arylene sulfide) which contains a step of polymerizing a sulfur source and a dihalo-aromatic compound in an organic amide solvent, said polymerization step containing a phase-separation polymerization step that the polymerization reaction is continued in the presence of a phase separation agent in a phase-separated state, wherein a monohalo-organic compound is added in a proportion of 0.005 to 20 mol per 100 mol of the charged sulfur source into the polymerization reaction system at the time a conversion of the dihalo-aromatic compound has reached 80 to 99% after initiation of the polymerization reaction and before the liquid phase becomes the phase-separated state to be reacted with a formed polymer, and the liquid phase within the polymerization reaction system is then converted to the phase-separated state to continue the polymerization reaction.