An object of the present invention is to provide a novel pharmaceutical agent for improving autism spectrum disorder, a pharmaceutical agent for improving a mental disease, or a supplement exerting an effect of improving social behaviors or developing sociality or an anti-anxiety and anti-stress effect or a functional food exerting such an effect. The present invention also provides a pharmaceutical agent for promoting the secretion of oxytocin and/or vasopressin in the brain. The above objects are achieved by a pharmaceutical agent for improving autism spectrum disorder, a pharmaceutical agent for improving a mental disease, or a supplement exerting an effect of improving social behaviors or developing sociality or an anti-anxiety and anti-stress effect or a functional food exerting such an effect, or a pharmaceutical agent for promoting the secretion of oxytocin and/or vasopressin, which comprises D-allulose as an active ingredient.