The present application provides: a composition for improving or preventing symptoms of human Parkinson's disease, multiple system atrophy or progressive supranuclear palsy, for example symptoms including at least tremors and/or forward-bending posture, or gait disorder, the composition including a hydrogen gas-containing gas as an effective ingredient； and a method for improving or preventing symptoms of Parkinson's disease, multiple system atrophy or progressive supranuclear palsy, which method comprises administering the composition to a human patient.
