The invention provides a method for treating ALS or suppressing the disease progress thereof, or treating symptoms caused by ALS or suppressing the disease progress thereof by administering an agent containing, as an active ingredient, 3-methyl-1-phenyl-2-pyrazolin-5-one or a physiologically acceptable salt thereof, to a patient that complies with specific criteria. The agent is administered by repeating a 14-day administration period and a 14-day drug holiday period, or by establishing an initial 14-day administration period and an initial 14-day drug holiday period and then repeating an administration period for 10 out of 14 days and a 14-day drug holiday period
