The purpose of this study is to evaluate the efficacy of TA-650 using Pediatric Crohn's Disease Activity Index (PCDAI) in pediatric patients with moderate to severe Crohn's disease after TA-650 administration at a dose of 5 mg/kg at week 0, 2, and 6, then every 8 week after week 14 up to week 46, and at a dose of 10 mg/kg if the effect is attenuated. The safety and pharmacokinetics are also evaluated.