Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder involving the systemic motor neurons, but autonomic nervous function is relatively well preserved. A few studies related to autonomic dysfunction have been reported, but autonomic dysfunction is rare in ALS. Moreover, dysautonomia symptoms are not prominent in patients with ALS. We present a 55-year-old male patient with ALS, who had acute severe hypertension and tachycardia crises, as well as sudden falls in his blood pressure. After he was diagnosed with ALS, he suddenly collapsed and was placed under mechanical ventilation. Several hypertensive attacks and dysautonomic signs then occurred. We successfully controlled the dysautonomia using diazepam and doxazocin mesylate, an alpha receptor antagonist.