The present invention provides a compound that has a high whitening effect and is excellent in safety and stability and provides an external preparation for skin comprising the same. The compound of the present invention is a 4-alkylresorcinol derivative represented by formula (1) or a salt thereof:wherein R1 is a branched or cyclic alkyl group of 3 to 7 carbon atoms or a linear alkyl group of 2 to 5 carbon atoms； R2 and R3 are each independently a hydrogen atom or a group represented by —P(O)(OR4)(OR5), and at least one of R2 and R3 is a group represented by —P(O)(OR4)(OR5)； and R4 and R5 are each independently a hydrogen atom or a linear or branched alkyl group of 2 to 5 carbon atoms.
