An object of the present invention is to provide an agent for improving a mental health disfunction or a composition for improving a mental health disfunction, and a food or drink composition for improving a mental health disfunction which are effective for improving a mental health disfunction, which are highly safe, and which can be continuously ingested on a daily basis, and this object is achieved by an agent for improving a mental health disfunction or a composition for improving a mental health disfunction, or a food or drink composition for improving a mental health disfunction, each comprising as an active ingredient a bacterium belonging to Bifidobacterium longum subsp. infantis.
