Inclusion Criteria:

• Patients with rheumatism who have moderate-to-severe pain
• Patients who have not been administered Ultracet or tramadol over the last one month
• Patients who have signed a consent form indicating that they understand the purpose of and procedures required for the study (As for minors between 12 and 20 years old, the patients' legally acceptable representatives' signature is also required.)

Exclusion Criteria:

• Patients who have experienced failure of tramadol therapy or discontinued Tramadol because of adverse events
• Patients with impaired physical function or disease which may cause drug absorption anomaly, excess storage and metabolic or elimination disorder
• Patients who meet any of the prohibitions of tramadol or acetaminophen {Patients who are hypersensitive to active ingredients of the study drug:

Patients who are addicted to drugs acting on central nervous system including alcohol, hypnotics, centrally acting analgesics, opiates and psychotropics, Patients with serious respiratory depression (The study drug may cause mild respiratory depression.), Patients with head injury and brain lesion who have the risk of mental fog, Patients who are taking an MAO inhibitor or discontinued it no more than 2 weeks ago, Patients with peptic ulcer and severe hematological anomaly, Patients with severe hepatic impairment, renal impairment or cardiac dysfunction, Patients with aspirin-induced asthma (asthmatic attacks induced by nonsteroidal anti-inflammatory drug), Patients with epilepsy which is not controlled by a drug}

• Patients who are pregnant or of childbearing potential during the study