The present invention mainly aims to provide a drug for the prophylaxis or treatment of androgen-independent prostate cancer, which is highly useful as a pharmaceutical agent. The present invention provides a drug for the prophylaxis or treatment of androgen-independent prostate cancer, containing a steroid C17,20 lyase inhibitor, particularly, a compound represented by the formula (I): wherein n is an integer of 1 to 3, and Ar is an aromatic ring optionally having substituent(s), or a salt thereof or a prodrug thereof.