The primary efficacy end points are: a) the change in score (baseline to Visit 5) for the Erectile Function domain score of the IIEF, b) change in response, relative to baseline, for sexual encounter profile (SEP) question 2, and c) change in response, relative to baseline, for SEP question 3. For DA-8159 tablets to be judged efficacious, the DA-8159 tablet groups must be shown superior to the placebo group on all three measures.