This Study is to Evaluate the Safety and Efficacy of Avanafil in the Treatment of Erectile Dysfunction.

Inclusion Criteria: 1. Male patients over 20 years old with a history of erectile dysfunction for at least 6 months prior to participation in the study 2. Patients in a stable relationship with 1 female partner 3. Patients whose sex partner is not in pregnancy or lactating, and is taking proper contraceptive 4. Patients who have voluntarily decided to participate in this clinical trial, and signed the informed consent form 5. Patients whose failure rate for sexual intercourse is more than 50% after attempts of sexual intercourse on more than 3 different days (once/day) at least during the 4-week Free run-in period 6. Patients whose EF domain score is less than 18 points (moderate to severe erectile dysfunction) in the IIEF questionnaire after the 4-week Free run-in period Exclusion Criteria: 1. Patients who have a spinal injury or have had a radical prostatectomy 2. Patients with anatomical malformations of the penis (example: angulation, fibrosis of corpus cavernosum, peyronies disease, etc.) 3. Patients who had surgery in the pelvic cavity within 6 months prior to participation in the study 4. Patients with neurogenic or endocrine (example: hyperprolactinemia, low testosterone, etc.) ED * Hyperprolactinemia: Serum prolactin ≥ 3 X ULN * Low testosterone: Total testosterone is less than the normal lower limit(testosterone is susceptible to daily changes, so enrollment is permitted after retesting before 11 am, only limited to once, when the number is 20% less than the normal lower limit.) 5. Patients with a major refractory psychiatric disorder (including major depression or schizophrenia) or significant neurological abnormalities (neurovascular disease) 6. Patients with alcohol addiction or persistent abuse of drugs of dependence 7. Patients with hepatic dysfunction or renal dysfunction as per the following: * Hepatic dysfunction: AST, ALT ≥ 3 X ULN * Renal dysfunction: Serum creatinine \> 2.0mg/dL 8. Diabetic patients whose HbA1c exceeds 12% 9. Patients with proliferative diabetic retinopathy 10. Patients who have had a stroke, TIA(Transient ischemic attack), MI(Myocardial Infarction) or fatal arrhythmia, or severe heart failure, unstable angina or who underwent coronary artery bypass grafting (CABG) within the last 6 months prior to participation in the study 11. Patients with hypotension (resting SBP/DBP in the sitting position is less than 90/50mmHg) or unregulated hypertension (resting SBP/DBP in the sitting position exceeds 170/100mmHg) 12. Patients with hematopathy, which can be a predisposition to priapism (sickle-cell disease, multiple myeloma, leukemia) 13. Patients with a known genetically degenerative retinopathy, including retinitis pigmentosa 14. Patients who have had experience with avanafil, viagra, cialis, levitra, yaila, zydena, mvix or other ED treatment within 2 weeks from participation in the study 15. Patients administered with the following medications: * Nitrate/Nitric oxide (NO) donors (example: nitroglycerin, isosorbide mononitrate, amyl nitrate/nitrite, sodium nitroprusside) * Androgens (example: testosterone), anti-androgen, trazodone * Anticoagulant (antiplatelet agents excluded) * Agents that significantly affect the CYP450 3A4 intermediary metabolism, such as erythromycin, intraconazol, ketoconazol, cimetidine, ritonavir, saquinavir, amprenavir, indinavir, and nelfinavir, etc. 16. Patients who have had a history of hypersensitivity to other PDE-5 inhibitors or who have not responded to them 17. Patients with primary hyposexuality 18. Patients who have taken other investigational products within 4 weeks before the study 19. For other reasons besides the aforementioned cases, patient whose participation is deemed inappropriate due to clinically significant findings according to the medical decision of the principal investigator or the study personnel