Inclusion Criteria:

- Written informed consent.

- Adequate oral intake.

- Histologically proved adenocarcinoma (colorectal cancer).

- Unresectable, recurrent and advanced colorectal cancer.

- At least 4 weeks since prior major surgery

- Age: 20 - 74 at enrollment.

- Performance Status (Eastern Cooperative Oncology Group [ECOG] scale): 0 - 2.

- No prior treatment (ex. radiation therapy, chemotherapy, hormonal therapy) to
advanced disease. Patients who received adjuvant chemotherapy more than 180 days
before enrollment can be allowed but those who received S-1 or Oxaliplatin containing
treatment shall be excluded.

- Proved presence of measurable lesions within 30 days before enrollment.

- Patients with the following function of bone marrow, liver and kidney based on the
laboratory values measured within 15 days before enrollment.

- Hemoglobin >_ 9.0g/dL

- WBC: LLN - 12,000/mm3

- Absolute granulocyte count >_ 1,500/mm3

- Platelets >_ 100,000/mm3

- Total Bilirubin <_ 1.5mg/dL

- AST(GOT) and ALT(GPT) <_ 100U/L

- ALP <_ 600U/L

- Creatinine <_ 1.0mg/dl

- Expected to survive more than 90 days after enrollment.

Exclusion Criteria:

- Patients who not received S-1 and Oxaliplatin as neoadjuvant or adjuvant
chemotherapies before enrollment.

- Contraindication to S-1, and serious hypersensitivity to oral Leucovorin.

- No other concurrent investigational therapy.

- Patients did who not received blood transfusion and hematogenesis stimulating agents
(ex. Granulocyte-Colony Stimulating Factor).

- Serious drug hypersensitivity.

- Prior history of peripheral neuropathy.

- Marked infection or inflammation (ex. patients with a fever of 38.0 degrees or
higher).

- Poorly-controlled diabetes, hypertension or hypercalcemia.

- Severe (inpatient care is needed) arrhythmia, heart disease or its history.

- Severe (inpatient care is needed) lung disease (ex. interstitial pneumonia or
pulmonary fibrosis).

- Psychiatric disorder requiring to receive treatment with antipsychotic drug.

- Fresh bleeding from the gastrointestinal tract.

- Requiring to drainage massive ascites, pleural effusion retention or pericardial
fluid.

- Extensive bone metastasis.

- Clinically suspicious brain metastasis or brain metastasis.

- Diarrhea (watery diarrhea).

- Simultaneously active double cancer.

- Pregnancy or nursing female patients and possibility (intent) to bear baby. Male
patients with intent to impregnate.

- Other patients evaluated to be inadequate to participate in the study by (sub)
investigators.