Provided is a method for efficiently separating nickel, cobalt and/or scandium, and impurities from an acidic solution containing impurities such as manganese, iron, zinc, and aluminum. A valuable-metal extracting agent of the present invention is expressed by general formula (1). In the formula, R 1 and R 2 each represent the same or different alkyl groups, R 3 represents a hydrogen atom or an alkyl group, and R 4 represents a hydrogen atom or a given group, other than an amino group, that bonds with an ± carbon as an amino acid. In general formula (1), the inclusion of a glycine unit, a histidine unit, a lysine unit, an asparagine acid unit, or a normal methylglycine unit is preferred.