The present invention provides a therapeutic agent for secondary hyperparathyroidism which comprises as an active component a vitamin D3 derivative represented by formula (1) or a medically acceptable solvate thereof.本發明係關於含有將下述式(1)所示維他命D3衍生物或其醫藥上可被許可的溶劑合物作為有效成分之次發性副甲狀腺機能亢進症治療劑。