Provided is an agent, said agent having an improved effect of enhancing NO production, for preventing or ameliorating vascular endothelial malfunction and symptoms that occur with the progress of vascular endothelial malfunction such as arteriosclerosis-related symptoms (for example, ischemic diseases such as myocardial infarction, angina, peripheral artery occlusion, etc.) or blood flow reduction-related symptoms (stiff shoulders, oversensitiveness to cold, swelling, erectile dysfunction, rough skin, exercise performance reduction caused by skeletal muscle hypoactivity, etc.). An NO production enhancer which comprises, as the active ingredients, citrulline or a salt thereof and glutathione or a salt thereof. An agent for preventing or ameliorating vascular endothelial malfunction, said agent comprising, as the active ingredients, citrulline or a salt thereof and glutathione or a salt thereof. An agent for preventing or ameliorating symptoms that occur with the progress of vascular endothelial malfunction, said agent comprising, as the active ingredients, citrulline or a salt thereof and glutathione or a salt thereof.
