Inclusion Criteria:

• The subject is an outpatient.
• The subject is 20 years of age or older at the time of consent to participate in the study.
• The subject's serum creatinine value is 5.0 mg/dl or less at the time of case registration.
• The inverse serum creatinine value, calculated using measurements at four or more time points during an observation period that occurs within 48 weeks of case registration, is decreasing, on average, according to linear-regression analysis performed at the case registration center.
• The subject's blood pressure is well controlled before the initial serum creatinine measurement during the observation period.
• The subject has been treated with an ACEI and/or ARB before the initial serum creatinine measurement during the observation period.
• The subject has undergone low-protein diet therapy (> 0.8 g/kg per day) before the initial serum creatinine measurement during the observation period.
• The subject has not changed the type or dose of medication for renal failure for 4 weeks prior to case registration.
• The subject has participated in thorough consultation and has been informed as to the purpose, description, expected adverse effects, and risks of this study according to the consent form, and has voluntarily signed the informed consent form.

Exclusion Criteria:

• The subject has a passage disorder of the gastrointestinal tract.
• The subject has been treated with Kremezin within the period from the initial measurement of the serum creatinine level prior to case registration to the time of study commencement.
• The subject has rapid progressive glomerular nephritis, hydronephrosis, occlusive urinary tract injury, drug-induced nephropathy, or transplanted kidney.
• The subject has complications such as severe hepatopathy, liver cirrhosis, severe infection, class III or above New York Heart Association (NYHA) congestive heart failure, severe arrhythmia, or unstable angina.
• The subject has had cardiac infarction, cerebral infarction, or cerebral hemorrhage within the past 6 months.
• The subject presents with severe nephrotic syndrome (serum albumin < 2 g/dl).
• The subject is currently pregnant, or plans to become pregnant during the study period.
• The subject abuses alcohol.
• The subject has a body weight less than 80% or more than 160% of the standard weight {[height(m)]^2 x 22}.
• The subject has significant difficulty in controlling his/her blood sugar level within 3 months of case registration (hemoglobin [Hb]A1c > 8.0% on one occasion).
• The subject has a progressive malignant tumor.
• The subject is not available for study visits at least once per 2 months to provide urine samples.
• The subject is inappropriate for participation in the study for other reasons, as determined by an investigator.