The purpose of the invention is to provide a medicinal agent which has good solubility and good oxidative-stress-mediated cell death suppressing activity, can exhibit excellent blood-brain barrier penetration properties, and is effective for the treatment and prevention of neurological diseases. The invention provides: an acylaminoimidazole derivative represented by general formula (I) or a salt thereof; and a medicinal agent and a therapeutic or prophylactic agent for neurological diseases, each of which comprises the derivative or the salt thereof as an active ingredient.