Provided is a novel drug which exhibits excellent effect of inhibiting expression of an ABC transporter protein, as well as improved safety. An ABC transporter protein expression inhibitor containing, as an active ingredient, a substance which inhibits expression of one or more genes selected from the group consisting of ARHGAP17, CTDSP2, DUSP1, IMPA2, RHOBTB3, SGK, UBE2H, INPP5F, MAP2K6, PPM1E, PRKAG2, PRKCD, PTPN21, UBE2B, UBTF, and ZNF259.