An object of the present invention is to demonstrate the existence of a heterodimer of somatostatin receptor subtype 1 (SSTR1) and somatostatin receptor subtype 4 (SSTR4) and also to provide a method for screening a factor that binds to such a heterodimer and the heterodimer that can be used in the screening method. A transformant expressing a heterodimer of somatostatin receptor subtype 1 and somatostatin receptor subtype 4, into which DNA encoding somatostatin receptor subtype 1 and DNA encoding somatostatin receptor subtype 4 have been introduced. A method for screening a compound that interacts with a heterodimer of somatostatin receptor subtype 1 and somatostatin receptor subtype 4, comprising selecting the compound that interacts with the heterodimer from test compounds.