The present invention provides a pharmaceutical that can be used widely for intractable neurological diseases, inflammatory diseases, etc. The immune cell activation inhibitor of the present invention contains bromovalerylurea or a derivative thereof. The immune cell activation inhibitor of the present invention can be used as a pharmaceutical for, for example: chronic neurological diseases such as Parkinson's disease and Alzheimer's disease； acute neurological diseases such as cerebral infarction and brain injury； and inflammatory diseases such as systemic inflammatory response syndromes.
