NOVELTY - A dehydrogenation catalyst comprises a complex (I) or (II), its isomer, or its salt as an active component. The complex comprises a bidentate ligand containing an aromatic heterocyclic 5-membered ring containing 2 or more nitrogen atoms, or a bidentate ligand containing an aromatic heterocyclic 5-membered ring containing 2 or more nitrogen atoms, and a 6-membered ring containing nitrogen atom(s).    USE - Catalyst is used for dehydrogenating formic acid and/or formate to manufacture hydrogen (all claimed) for use in petroleum refinement and ammonia manufacture, and as fuel in fuel cells used for transport applications.    ADVANTAGE - The catalyst enables simple dehydrogenation of formic acid and/or formate to manufacture high-pressure carbon-monoxide-free hydrogen even under high-temperature reaction conditions in a high-concentration formic acid solution, with high energy efficiency and selectivity. High catalytic activity and catalyst durability are maintained over a long period of time. Hydrogen can be supplied as a fuel of fuel cell, without using a gas reforming apparatus by dehydrogenation of formic acid.    DETAILED DESCRIPTION - A dehydrogenation catalyst comprises a complex of formula (I) or (II), its isomer, or its salt as an active component. The complex comprises a bidentate ligand containing an aromatic heterocyclic 5-membered ring containing 2 or more nitrogen atoms, or a bidentate ligand containing an aromatic heterocyclic 5-membered ring containing 2 or more nitrogen atoms, and a 6-membered ring containing nitrogen atom(s).    M1,M2=transition metal of iridium, rhodium, ruthenium, cobalt, osmium, nickel, iron, palladium or platinum;    X1-X16=N or C;    R1-R13=H, alkyl, hydroxy, alkoxy, nitro, halo, sulfonyl, carboxylic acid group, alkylamino, phenyl, or may form ring with adjacent R, with substituent(s);    L1,L2=aromatic anion ligand or aromatic ligand (both optionally substituted);    Z1,Z2=optional arbitrary ligands;and    m,n=positive integer, 0, or negative integer.    INDEPENDENT CLAIMS are included for the following:    (1) dehydrogenation of formic acid and/or formate, by reacting a solution containing formic acid and/or formate in the presence of the catalyst; and    (2) manufacture of hydrogen by dehydrogenation of formic acid and/or formate.