Disclosed is a means for treatment of breast cancer and/or mastitis by topically administering a non-steroidal antiphlogistic analgetic agent and/or an anti-cancer agent to allow the agent to reach a mammary gland with good efficiency. Specifically, disclosed is an iontophoresis preparation for use in the treatment of breast cancer and/or mastitis comprising a non-steroidal antiphlogistic analgetic agent and/or an anti-cancer agent as an active ingredient. The preparation can be used in such a manner that a donor for the preparation is applied onto a nipple and power is then applied to the donor to induce the topical application of the active ingredient from the nipple into a mammary gland.