An object of the present invention is to provide molecules that bind to a target molecule in a pH dependent manner and a screening method for selecting such molecules. Provided is a screening method for selecting peptides that bind to a target molecule at a first pH and do not bind thereto at a second pH, including a step of preparing a peptide library in which each mRNA contains at least one special amino acid that undergoes a pH-dependent change in the charge of the side chain thereof, a step of bringing the peptide library into contact with the target molecule and incubating them under the first pH condition and selecting peptides that bind to the target molecule, and a step of selecting, from the peptides which have bound to the target molecule, peptides that do not bind to the target molecule under the second pH condition.
