The purpose of this study is to verify the effectiveness, safety and pharmacokinetics of fentanyl transdermal matrix patches containing either 12.5 mcg/hr, 25 mcg/hr, or 50 mcg/hr in Japanese patients with cancer pain who have been switched from minimum amount of existing morphine preparations, such as equivalent to less than 45 mg/day of oral morphine, or oral oxycodone preparations equivalent to less than 30 mg/day.