An objective of the present invention is to provide target tissue-specific antigen-binding molecules, antigen-binding molecules whose antigen-binding activity varies depending on the concentration of an unnatural compound, libraries comprising a plurality of the antigen-binding molecules which are different from one another, pharmaceutical compositions comprising the antigen-binding molecules, methods of screening for the antigen-binding molecules, and methods for producing the antigen-binding molecules. The present inventors created antigen-binding domains whose antigen-binding activity varies depending on the concentration of a small molecule compound or antigen-binding molecules containing an antigen-binding domain, and libraries comprising a plurality of the antigen-binding domains which are different from one another or antigen-binding domains, and demonstrated that the above-noted objective could be achieved by using the libraries. Various diseases originating from target tissues can be treated in a target tissue-specific manner by using the antigen-binding molecules of the present invention.
