Primer sets for amplifying target regions containing sites to be detected in the UGT1A1 gene by a gene amplification method are provided, wherein the primer sets can amplify the regions specifically Three pairs of primer sets are used including forward primers consisting of the base sequences of SEQ ID NOs: 4 or 81, 21, and 42 as well as reverse primers consisting of the base sequences of SEQ ID NOs: 13 or 91, 29 and 48, respectively. The use of these primer sets makes it possible to amplify three target regions including parts where three types of polymorphisms (UGT1A1*6, UGT1A1*27, and UGT1A1*28) of the UGT1A1 gene are generated, respectively, in the same reaction solution at the same time.