The present invention provides a synthetic peptide capable of inducing an antibody to an autoantigen, and specifically, provides: a multiplexed same type-antigenic peptide having a dendritic core and B-cell recognition peptides, wherein the multiplexed same type-antigenic peptide comprises 4 to 8 B-cell recognition peptides of the same type that are bound to the terminal ends of the dendritic core directly or via a spacer, and each B-cell recognition peptide is bound to the terminal end of the dendritic core directly or via a spacer; an antibody production-inducing agent having the peptides; and a method for producing the peptide.