The purpose of this study is to evaluate the safety and effectiveness of golimumab in patients with active rheumatoid arthritis despite Methotrexate therapy. Another objective is to evaluate the pharmacokinetics of golimumab.

This clinical study is scheduled to be performed for the purpose of evaluating the safety and effectiveness of golimumab (CNTO148) administered in combination with stable dose (6-8mg/week) of methotrexate (MTX) to patients with rheumatoid arthritis (RA). CNTO148 50 mg group: CNTO148 50 mg SC injections every 4 weeks from the first administration until week 152. If early escape, 100 mg SC injections every 4 weeks from week 16 until week 152. CNTO148 100 mg group: CNTO148 100 mg SC injections every 4 weeks from the first administration until week 152 whether early escape or not Placebo group: Placebo SC injections every 4 weeks from the first administration until week 20 and then CNTO148 50mg SC injections every 4 weeks from week 16 until week 152

Inclusion Criteria:

• Patients diagnosed with rheumatoid arthritis at least 3 months prior to registration and who are definitely identified as having rheumatoid arthritis, at the time of informed consent, according to the criteria for classification established by the American College of Rheumatology (1987)
• Patients in whom MTX therapy (>= 6 mg/week) was started more than 3 months before the first administration and who have been treated with MTX at a stable dose (6-8 mg/week) for at least 4 weeks before the first administration
• Patients having at least 4 swollen joints and at least 4 tender joints at the time of registration and immediately before the first administration.

Exclusion Criteria:

• Patients with a history of hypersensitivity to human immunoglobulin proteins or other ingredients of golimumab
• Patients who have previously experienced or are suffering from any of the following diseases: (i) Collagen diseases other than rheumatoid arthritis, (ii) Latent or active granulomatous infections such as histoplasmosis and coccidioidomycosis, (iii) Felty syndrome, etc
• Patients with a severe, advanced, or poorly controlled disease in any of the kidney, liver, blood, gastrointestinal system, endocrine system, lung, heart, nervous system, psychiatric system, and brain.