The purpose of the present invention is to provide: a peptide having an affinity for silicon nitride; a polynucleotide encoding the peptide; an expression vector for expressing the peptide having an affinity for silicon nitride; an expression vector for expressing a peptide fusion protein that comprises the peptide having an affinity for silicon nitride and a target protein; a transformant obtained by introducing the expression vector into a host cell; a peptide fusion protein obtained from the transformant; a silicon nitride substrate to which a peptide having an affinity for silicon nitride has been bonded; a method for immobilizing a target protein to a silicon nitride substrate; a composition for immobilizing a target protein to a silicon nitride substrate, the composition comprising a peptide having an affinity for silicon nitride; and a linker for immobilizing a target protein to a silicon nitride substrate, the linker comprising a peptide having an affinity for silicon nitride. The invention involves a peptide having an affinity for silicon nitride, the peptide comprising (1-1) a peptide having the amino acid sequence of one of SEQ ID NOS: 1, 2 and 23 to 27, (1-2) a peptide that has an affinity for silicon nitride and comprises an amino acid sequence obtained by deleting, adding, and/or substituting one or more amino acids in one of the amino acid sequences indicated in (1-1), or a fragment of one of the peptides.