Disclosed is an anti-foot-and-mouth disease virus agent for an animal belonging to the Family Suidae, which comprises 3-oxo-3,4-dihyro-2-pyrazincarboxamide or a salt thereof. The agent is extremely useful for the prevention or treatment of food-and-mouth disease in an animal belonging to the Family Suidae. Also disclosed is an anti-foot-and-mouth disease virus agent for sheep, which comprises 3-oxo-3,4-dihyro-2-pyrazincarboxamide or a salt thereof. The agent is extremely useful for the prevention, therapy or the like of food-and-mouth disease in sheep.