Provided are a preventive and/or therapeutic agent for a disease associated with the expression of IDO, and a pharmaceutical composition for treating an IDO-positive tumor. A preventive and/or therapeutic agent for a disease associated with the expression of IDO, which comprises a compound that inhibits HSP90 as an active ingredient, and a pharmaceutical composition for treating an IDO-positive tumor.ＩＤＯの発現が関与する疾患の予防及び／又は治療剤、並びにＩＤＯ陽性腫瘍の治療用医薬組成物の提供。 ＨＳＰ９０を阻害する化合物を有効成分とするＩＤＯの発現が関与する疾患の予防及び／又は治療剤、並びにＩＤＯ陽性腫瘍の治療用医薬組成物。
