Provided is an agent for improving mitochondrial function including a hydroxycitric acid derivative represented by the following Formula (I) or a salt thereof, as an active ingredient [(In Formula (I), R 1 and R 2 each independently represent a hydrogen atom or any one group selected from the group represented by the following Formula (Ia) (here, R 1 and R 2 do not represent hydrogen atoms at the same time), X 1 to X 3 each independently represent a nitrogen or an oxygen atom, and R 3 , R 4 , R 5 , R 3 , R 4 , and R 5 each independently represent a hydrogen atom, or a chained hydrocarbon group (here, in a case where X 1 , X 2 , and X 3 each independently represent an oxygen atom, corresponding R 3 , R 4 , or R 5 does not exist). In Formula (Ia), R 6 to R 8 each independently represent a hydrogen atom, an aryl group, or a chained hydrocarbon group having 1 to 30 carbon atoms].
