This clinical study is designed to evaluate the efficacy and safety of silodosin in a 12 week treatment of patients with severe urinary disorders associated with benign prostatic hyperplasia (BPH).

Inclusion Criteria:

• Is at least 50 years old
• Has a urinary disturbance associated with severe BPH and has a total IPSS score 20 or higher
• Has a QoL score of 3 or higher
• Has a urine volume of 120mL or greater and a Qmax of below 15mL/sec
• Has a PRV of below 100mL
• Voluntarily decides to participate in this trial and sign with informed consent form

Exclusion Criteria:

• Has been administered silodosin
• Has been administered an α1A-adrenoceptor blocker within one month
• Has been prescribed antiandrogens except 5α-reductase inhibitors within a year
• Has had phytotherapy within 3 months
• Has had prostatectomy
• Has had intrapelvic radiation therapy
• Has had transurethral microwave hyperthermia of transurethral needle ablation
• Is suspected to have implications that are likely to affect urine passing such as neurogenic bladder, bladder calculus or active urinary tract infection (UTI).
• Is conducting self-catherterization
• Has a renal impairment with a serum creatinine of 2.0mg/dL or greater
• Has severe hepatic disorders (hepatic insufficiency, cirrhosis, jaundice, hepatoma) or has a total bilirubin of 2.5mg/dl or higher or has AST/ALT 2.5 times higher than the normal (upper) level
• Has suffered from a severe arrhythmia, cardiac failure, cardiac infarction, unstable angina, cerebral infarction within 6 months
• Has experienced allergy to α1 receptor blockers
• Has orthostatic hypotension around the time of Screening Visit
• Has participated in other clinical trials within 8 weeks prior to Screening Visit
• Has a Prostate specific antigen(PSA) of higher 10ng/mL or has been diagnosed with tumor identified by a biopsy even though he has a PSA of lower 10ng/mL (Patient who has been administered 5α-reductase inhibitors for more than 3 months are presumed to have 2 times higher than their actual PSA levels)
• Has been taking unstable dosing of 5α-reductase inhibitors like finasteride or dutasteride for the past 3 months or is expected to change the dosage during the trial.