Mycophenolate Mofetil in Patients With Progressive Idiopathic Membranous Nephropathy

Inclusion Criteria: 1. Patients with idiopathic membranous nephropathy 2. The duration of disease is less than twelve months 3. Patients with persistent proteinuria more than 8 grams per day 4. Patients who provided informed consent 5. The cases that satisfy more than three of following items even if proteinuria is less than 8 grams per day: * eGFR \< 60 ml/min/1.73m2 * Hypertension (BP above 140/90mmHg or BP above 120/80 in patients taking anti-hypertensive agents) * 24 hours urine protein or spot urine protein/creatinine ratio \> 5.0 g/day * Serum albumin (g/dL) \< 3.0 * Selectivity index \> 0.2 Exclusion Criteria: 1. Severe digestive organ disease 2. Allergy history to clinical trial medication and acute or chronic allergy for 4 weeks recently. 3. Clinical history of treatment with other immunosuppressive medication 4. Probability of pregnancy, breast feeding woman 5. Uncontrolled hypertension (more than 160/100mmHg) 6. Uncontrolled systemic disease 7. Drug addiction or alcoholics within 6 months 8. eGFR is less than 30ml/min at screening 9. Abnormal liver function test (more than 3 times above compared with normal value) 10. Absolute neutrophil count \<1,500/mm3 or leukocyte \<2,500/mm3 or platelets \<100,000/mm3 11. Secondary membranous nephropathy 12. Expected life expectancy is less than 1 year