Disclosed is a process for producing a phosphine derivative from a phosphine oxide derivative, which comprises the following steps: (I) mixing a phosphine oxide derivative represented by formula (1) with a chlorinating agent in a polar organic solvent to cause the reaction between these components; and (II-1) adding a salt of a metal having an ionization tendency equal to or lower than that of aluminum to the reaction mixture and carrying out the reductive reaction in the presence of aluminum or (II-2) subjecting the reaction mixture to electrolytic reduction, thereby producing a phosphine derivative represented by formula (2). ArnR3-nP═O (1) ArnR3-nP (2) In formulae (1) and (2), Ar represents an aryl group such as a phenyl group, a phenyl group having a substituent, a heteroaromatic ring group, and a heteroaromatic ring group having a substituent; R represents an aliphatic hydrocarbon group or an aliphatic hydrocarbon group having a substituent; and n represents an integer of 0 to 3.