The thin-film patterning method for a magnetoresistive device comprises forming a functional layer on a substrate; forming a first mask layer above the functional layer; forming a patterned resist on the first mask layer; etching the first mask layer by using the resist; removing the resist; forming a second mask layer by atomic layer deposition, the second mask layer covering a step defined by an edge of the first mask layer; dry-etching the second mask layer in a thickness direction of the substrate so as to leave the second mask layer on a side face of the step; removing the first mask layer so as to expose the functional layer under the first mask; and dry-etching the functional layer by using the second mask layer.