This is a 12-week, prospective double-blinded, randomized, multicenter study of placebo, 120 Unit, and 240 unit of botulinum toxin A ( Dysport ® ) injection for patient with a diagnosis of Migraine without aura according to International Headache Society criteria. It is designed to evaluate the efficacy, safety, tolerability and optimum dose of Botulinum toxin type A (Dysport ®)injection for migraine without aura prophylaxis.