The purpose of this study is to verify the effectiveness, and safety in Japanese patients with chronic intractable pain after 4-week medication of fentanyl transdermal matrix patches containing either 12.5 mcg/hr, 25 mcg/hr, 50 mcg/hr, 75 mcg/hr, or 100 mcg/hr, who have been switched from existing formulations, such as codeine, morphine hydrochloride, or fentanyl injectable. Furthermore, the safety and effectiveness of long term treatment such as 48 weeks are to be assessed, if possible.