A metal complex containing a ruthenium ion or an osmium ion, and a tridentate aminodicarbene ligand, the tridentate aminodicarbene ligand having one secondary amino group and two heterocyclic carbene groups sandwiching the amino group, the heterocyclic carbene groups being represented by Formula L 1 and/or Formula L 2: wherein R 1 to R 3 are identical or different and each independently represents hydrogen, halogen, hydroxyl, oxyanion (-O -), hydroxycarbonyl, nitro, cyano, sulfo, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclic, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkoxycarbonyl, optionally substituted carboxylic anhydride, optionally substituted amino, optionally substituted acyloxy, or optionally substituted sulfonyloxy, or R 1 and R 2, and/or R 2 and R 3, taken together, form optionally substituted divalent hydrocarbon or optionally substituted divalent heteroatom-containing hydrocarbon; and R 4 to R 8 are identical or different and each independently represents hydrogen, halogen, hydroxyl, oxyanion (-O -), hydroxycarbonyl, nitro, cyano, sulfo, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclic, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkoxycarbonyl, optionally substituted carboxylic anhydride, optionally substituted amino, optionally substituted acyloxy, or optionally substituted sulfonyloxy, or R 5 and R 6, and/or R 7 and R 8, taken together, form optionally substituted divalent hydrocarbon or optionally substituted divalent heteroatom-containing hydrocarbon, wherein the tridentate aminodicarbene ligand is represented by Formula: wherein Q 1 and Q 2 are identical or different and each represents optionally substituted C 1-5 alkylene or optionally substituted C 3-15 cycloalkylene, and two Ls are identical or different and each represents L 1 or L 2. wherein R 1 to R 3 are identical or different and each independently represents hydrogen, halogen, hydroxyl, oxyanion (-O -), hydroxycarbonyl, nitro, cyano, sulfo, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclic, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkoxycarbonyl, optionally substituted carboxylic anhydride, optionally substituted amino, optionally substituted acyloxy, or optionally substituted sulfonyloxy, or R 1 and R 2, and/or R 2 and R 3, taken together, form optionally substituted divalent hydrocarbon or optionally substituted divalent heteroatom-containing hydrocarbon; and R 4 to R 8 are identical or different and each independently represents hydrogen, halogen, hydroxyl, oxyanion (-O -), hydroxycarbonyl, nitro, cyano, sulfo, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl, optionally substituted heterocyclic, optionally substituted alkoxy, optionally substituted aryloxy, optionally substituted alkoxycarbonyl, optionally substituted carboxylic anhydride, optionally substituted amino, optionally substituted acyloxy, or optionally substituted sulfonyloxy, or R 5 and R 6, and/or R 7 and R 8, taken together, form optionally substituted divalent hydrocarbon or optionally substituted divalent heteroatom-containing hydrocarbon, wherein the tridentate aminodicarbene ligand is represented by Formula: wherein Q 1 and Q 2 are identical or different and each represents optionally substituted C 1-5 alkylene or optionally substituted C 3-15 cycloalkylene, and two Ls are identical or different and each represents L 1 or L 2.