Lacosamide is administered for patients with amyotrophic lateral sclerosis (ALS). This clinical trial is open-label, single group and before and after comparison study. Dosage of lacosamide is increased from 100mg to 400mg for 4 weeks. Safety of lacosamide administration in ALS is primary endpoint. Nerve excitability, fasciculation and muscle cramp are investigated before and after administration for secondary endpoints.