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), R1 and R2 each independently represent a hydrogen atom or any one group selected from the group represented by the following Formula (Ia) (here, R1 and R2 do not represent hydrogen atoms at the same time), X1 to X3 each independently represent a nitrogen or an oxygen atom, and R3, R4, R5, R3′ R4′, and R5′ each independently represent a hydrogen atom, or a chained hydrocarbon group (here, in a case where X1, X2, and X3 each independently represent an oxygen atom, corresponding R3′, R4′, or R5′ does not exist). In Formula (Ia), R6 to R8 each independently represent a hydrogen atom, an aryl group, or a chained hydrocarbon group having 1 to 30 carbon atoms].
