This is a randomized (study drug assigned by chance), double-blind (neither the patient nor the study staff will know the identity of the study drug assigned to each patient), multicenter study to evaluate the safety and efficacy of orally (by mouth) administered R331333 (referred to as JNS024 extended release \[ER\] capsules or CG5503) in dosages of 25 mg to 200 mg twice daily compared with orally administered capsules of oxycodone controlled release (CR) in dosages of 5 mg to 40 mg twice daily over 4 weeks in Japanese and Korean patients with moderate to severe chronic malignant tumor-related cancer pain who require around-the-clock opioid therapy (treatment with narcotic analgesics or pain relievers) and are dissatisfied with the pain relief they are experiencing from current treatment. The active control, oxycodone CR, is being used in this study because it is an opioid analgesic approved for the treatment of moderate to severe pain. Approximately 212 Japanese patients and approximately 100 Korean patients who meet screening criteria for the study will be enrolled in the study and will enter the titration period of the study where they will receive a starting dosage of either JNS024 ER 25 mg twice daily or oxycodone CR 5 mg twice daily. The dose of study drug for each patient will be titrated (increased) to the optimal dose until sufficient analgesia (pain relief) is achieved (ie, up to a maximum dose of JNS024 ER 200 mg twice daily or Oxycodone CR 40 mg twice daily). When the dosage of study drug is increased, the safety will be confirmed at the study visit or by telephone on the day after the dose is increased. Once an optimal dose of study drug is determined, the patient will continue to receive that dose during the maintenance period in the study. Patients will participate in the study for total of approximately 6 weeks; during this time patients will receive study drug for 4 weeks (titration and maintenance periods combined). During the study, if a patient experiences breakthrough pain (pain that occurs for short periods of time between doses of study drug), treatment with rescue medication (morphine immediate release \[IR\] 5 mg) will be given. In addition, patients will be allowed to continue to take stable doses of non-opioid analgesics (non-narcotic pain medications for mild to moderate pain) that they were taking at the time of study entry and may reduce the dosage or discontinue their use during the study. During the study, blood samples will be collected from patients at protocol-specified time points to determine the concentration of study drug after administration. The safety of patients will be monitored during the study by evaluating adverse events and findings from clinical laboratory tests, physical examinations, vital signs measurements, and electrocardiogram (ECG) measurements reported. The primary outcome measure in the study will be the change from baseline to the last 3 days of study drug administration in the average pain intensity score using an 11 point numerical rating scale (NRS). Patients will receive R331333 (referred to as JNS024 ER or CG5503) by mouth with or without food at a starting dose of 25 mg twice daily to be increased if necessary to a maximum dose of 200 mg twice daily for a total of 4 weeks (titration and maintenance periods combined) OR double-blind oxycodone CR by mouth with or without food at a starting dose of 5 mg twice daily to be increased if necessary to a maximum dose of 40 mg twice daily for a total of 4 weeks.