It is an object of the present invention to provide a novel pharmaceutical agent or method for treating ALS or suppressing the disease progress thereof, or treating symptoms caused by ALS or suppressing the disease progress thereof, wherein the agent can be administered particularly to patients obtaining high therapeutic effects, among ALS patients who require treatments. According to the present invention, there is provided a pharmaceutical agent for treating amyotrophic lateral sclerosis or suppressing the disease progress thereof or treating symptoms caused by amyotrophic lateral sclerosis or suppressing the disease progress thereof, which comprises, as an active ingredient, 3-methyl-1-phenyl-2-pyrazolin-5-one or a physiologically acceptable salt thereof, wherein 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, and wherein a patient administered with the agent complies with specific criteria.
