All subjects, who are judged to be suitable to the clinical trial after 4-week free run-in period was completed, should be administered with Avanafil 100mg(study group) or placebo 100mg(control group) for the first 4 weeks after randomization. When there are no moderate to severe adverse events at the 4 weeks evaluation after administration, and when it is decided by the researcher that the effect of Avanafil or placebo 100mg against erectile dysfunction is insufficient, a dosage increase to 200mg is executed. For subjects with a sufficient improvement effect on ED at 100mg, no dosage increase is allowed, and the previous 100mg administration should be maintained until the termination of the study.