An object of the present invention is to provide an agent for treating or preventing vasospasm. An object of the present invention is to provide an agent for treating or preventing cerebral vasospasm as well as arterial vasospasm. Further, an object of the present invention is to provide an agent for treating or preventing cerebral ischemia and cerebral infarction.The above problems are solved by an agent for treating and preventing vasospasm, cerebral ischemia, or cerebral infarction, comprising trehalose as the active ingredient. It is possible, by using such a trehalose-comprising agent, to suppress phenomena such as contraction of blood vessel and thickening of tunica intima and tunica media and to prevent or treat vasospasm and vasospasm-dependent diseases.
