This is a multi-center (when more than one hospital or medical school team work on a medical research study), double-blind (test or experiment in which neither the person giving the treatment nor the participant knows which treatment the participant is receiving), placebo-controlled (an inactive substance; a pretend treatment [with no drug in it] that is compared in a clinical trial with a drug to test if the drug has a real effect), parallel group comparison study. The total duration of the study will be 11 weeks and consists of 4 periods; a pre-observation period (4 weeks), open-label period (2 weeks), double-blind period (4 weeks) and follow-up period (1 week). Participants will receive tramadol hydrochloride plus acetaminophen tablets orally 4 times daily for 2 weeks with no less than 4-hour intervals (up to 8 tablets per day) during the open-label period and the dose will be fixed for each participant in the latter 1 week. During the double-period participants will receive tramadol hydrochloride plus acetaminophen tablets or placebo at the same dose as used for the latter 1 week of the open-label period for up to 4 weeks. Efficacy will be primarily evaluated by number of participants with insufficient pain relief after the start of double-blind period. Participant's safety will be monitored throughout the study.