The purpose of this study is to confirm the efficacy and the safety of Avanafil 100mg, 200mg or placebo administered orally for 12 weeks in patients with erectile dysfunction. The efficacy is evaluated by IIEF, SEP Q2 and Q3 and GEAQ and the safety is evaluated by laboratory tests, vital signs, physical examination and adverse events.

Inclusion Criteria:

• male subjects aged 19 to 70 with history of erectile dysfunction for at least 6 months
• subjects have stable monogamous relationships
• their partners are free from pregnancy and lactation and well prevent conception
• subjects consented to participate in the clinical study in writing
• subjects attempted sexual intercourse at least 4 times in separate days during 4 weeks' free run-in period, and failure rate is over 50%

Exclusion Criteria:

• history of spinal cord injury or radical prostatectomy
• subjects whose penises are anatomically deformed
• erectile dysfunction due to neurogenic or endocrine cause
• subjects who have uncontrolled major psychiatric disorder and do not accept therapies or have significant neurological abnormalities
• history of cancer chemotherapy within 1 year
• subjects who are addicted to alcohol or have continuously misused dependent drugs
• subjects who have hepatic dysfunction(GOP,GPT ≥ 3xUNL) or renal dysfunctions(serum creatinine > 2.0)
• subjects who have uncontrollable diabetes(FPG>180)
• subjects sho have proliferative diabetic retinopathy
• history of stroke, transient ischemic attacks, myocardial infarction, heart failure that needs to be medically treated, unstable angina or fatal arrhythmia or coronary artery bypass graft within 6 months
• serious hypotension or uncontrollable severe hypertension
• hematological disorders that is likely to be developed into priapism such as sickle cell disease, multiple myeloma, leukemia
• subjects who have retinitis pigmentosa
• subjects who suffered from serious GI bleeding disorder within 1 year
• subjects who took other PDE5 inhibitors or ED therapies within 2 weeks
• subjects who use non-concomitant medications(Nitrate/NO donors, Androgens, anti-androgen, trazodone, Anticoagulant,over-the-counter drugs known to inhibit the activity of CYP3A4)
• history of hypersensitivity to the PDE5 inhibitors or not responded to them
• subjects who have hypoactive sexual desire
• subjects who have no intention of having sexual intercourses 4 times in separate days during 4 weeks' free run-in period
• subjects who took other investigational products within 30 days before this clinical study
• subjects who are judged to be unsuitable to the clinical study by other reasons