Inclusion Criteria:

- Histologically documented colorectal adenocarcinoma

- Age over 18 years old

- Performance status (ECOG scale): 0-2

- Measurable or evaluable disease

- Patients can take food and drugs orally

- Adequate organ functions

- Life expectancy ≥ 3 months

- Patients should sign a written informed consent before study entry

Exclusion Criteria:

- Tumor type other than adenocarcinoma

- Second primary malignancy

- Prior systemic therapy (for instance, cytotoxic chemotherapy or active/passive
immunotherapy) for advanced or metastatic colorectal cancer

- Adjuvant or neo-adjuvant treatment for non-metastatic (M0) disease has been completed
within 6 months prior to initiation of study treatment.

- Prior radiotherapy was administered to target lesions selected for this study, or
radiotherapy to the non-target lesions has been completed within 4 weeks before
randomization.

- Presence of CNS metastasis

- Obvious peritoneal seeding or bowel obstruction disturbing oral intake

- Symptomatic peripheral neuropathy

- Major surgery within 4 weeks prior to study treatment start, or lack of complete
recovery from the effects of major surgery. The patient received curative operation
or RFA for metastatic disease.

- Serious illness or medical conditions

- Receiving a concomitant treatment with drugs interacting with S-1, capecitabine or
oxaliplatin, as follows;flucytosine, a fluorinated pyrimidine antifungal agent
phenytoin warfarin etc.

- Received any investigational drug or agent/procedure, i.e. participation in another
trial within 4 weeks before beginning treatment with study drug.

- Pregnant or lactating woman

- Women of child bearing potential not using a contraceptive method

- Sexually active fertile men not using effective birth control during medication of
study drug and up to 6 months after completion of study drug if their partners are
women of child-bearing potential

- Any patients judged by the investigator to be unfit to participate in the study