A glucokinase activator is provided; and a remedy and/or a preventive for diabetes, or a remedy and/or a preventive for diabetes such as retinopathy, nephropathy, neurosis, ischemic cardiopathy, arteriosclerosis, and further a remedy and/or a preventive for obesity are provided.A glucokinase activator characterized by containing a 2-heteroaryl-substituted benzimidazole derivative of a general formula (I-0) or its pharmaceutically-acceptable salt: ##STR00001## [in the formula, X represents a carbon atom or a nitrogen atom; X.sub.1, X.sub.2, X.sub.3 and X.sub.4 each independently represent a carbon atom or a nitrogen atom; the ring A represents a 5- or 6-membered nitrogen-containing aromatic hetero ring of a formula (II): ##STR00002## (in the formula, X represents a carbon atom or a nitrogen atom); R.sup.1 represents an aryl, etc.; R.sup.2 represents a hydroxy, etc.; R.sup.3 represents a --C.sub.1-6 alkyl, etc.; R.sup.4 represents a --C.sub.1-6 alkyl, etc.; X.sub.5 represents --O--, etc.; a indicates an integer of 1, 2 or 3; q indicates an integer of from 0 to 2; m indicates an integer of from 0 to 2].