To provide a sleep-ameliorating medicine that directly act on the sleeping mechanism to show the sleeping induction and is very effective for treatment and prevention of hypnagogic disorder, deep sleep disorder, middle wakening, or early wakening.

This sleep-ameliorating agent or sleeping disorder ameliorating agent includes, as active ingredients, vitamin B12s, activation type vitamin B12 or mecobalamin. In this case, vitamin B12s means other activation type mecobalamin (methyl B12), cyanocobalamin, hydroxocobalamin or the like in addition to vitamin B12.