Z-206 Phase III Clinical Trial -Investigation on the remission–maintaining effect in patients with Crohn's disease in remission phase-

INTERVENTION: Z‐206 group:Three tablets of Z‐206 400mg tablet, 4 tablets of Pentasa placebo tablet per time (total 7 tablets). 3 times a day (t.i.d.) after each meal for 48 weeks. Mesalazine group:Four tablets of Pentasa 250mg tablet, 3 tablets of Z‐206 placebo tablet per time (total 7 tablets). 3 times a day (t.i.d.) after each meal for 48 weeks. CONDITION: Patients with Crohn's disease in remission phase PRIMARY OUTCOME: Recurrence rate; Remission maintenance period; QOL (IBDQ) INCLUSION CRITERIA: 1)Patients whose Crohn's Disease Activity Index (CDAI) is less than 150 are defined to be in remission phase. 2)Patients whose lesion is mainly observed in the end of ileum or lower part. 3)Outpatients with age of 16 or older and 64 or younger at the time of obtaining informed consents (however, no restriction on sex). 4)Patients who understand the substances of this clinical trial and can give consent to participate in this clinical trial in writing. In a case of a patient with age below 20 at the time of obtaining informed consent, a patient for whom consent can be obtained from his or her custodian.