Inclusion Criteria:  Adults aged ≥ 19 years to ≤ 70 years  Patients with moderate-to-severe active Crohn's disease or ulcerative colitis who are unresponsive to, become unresponsive to, or have no tolerability to universal treatment (with corticosteroids, immunomodulators, etc.)  CDAI (Crohn's Disease Activity Index) ≥ 220 for Crohn's disease Complete Mayo score ≥ 6 for ulcerative colitis  Exclusion Criteria:  A history of total colectomy Acute severe UC(Ulcerative Colitis) A potential for a bowel resection surgery within 3 months Pregnancy and breastfeeding Prior use of any biologics including anti-TNFs, ustekinumab, and tofacitinib A history of solid cancer and blood cancer within 5 years Positive for active or latent tuberculosis (However, screening is possible if active tuberculosis is excluded and after at least 4 weeks of latent tuberculosis treatment.) Active severe infections such as sepsis, cytomegalovirus, listeriosis, and opportunistic infections such as progressive multifocal leukoencephalopathy (PML). Hypersensitivity to vedolizumab or its substances (e.g., dyspnoea, bronchospasm, redness, and increased heart rate) Experience of treatment with a drug or a medical device due to participation in another clinical trial within 3 months from the date of consent  A woman of childbearing potential who has a positive pregnancy test (Urine-hCG or Serum hCG) at a screening visit or does not agree to use at least one of medically acceptable, effective contraceptive methods*. However, females who reached menopause at least one year ago or turned out infertile due to an operation should be excluded.  *Effective contraceptive methods: intrauterine devices (e.g., IUD, mirena), dual barrier methods (diaphragm or condom/femidom + spermicide), and parenteral contraceptives. Continuing only sexual abstinence is not viewed as an acceptable method.  A woman of childbearing potential who neither practices adequate contraception nor agrees to continue its use for at least 18 weeks after the last dose of the study drug. Those decided by the investigator to be not eligible for this study