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: [in the formula, X represents a carbon atom or a nitrogen atom; X1, X2, X3 and X4 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): (in the formula, X represents a carbon atom or a nitrogen atom); R1 represents an aryl, etc.; R2 represents a hydroxy, etc.; R3 represents a —C1-6 alkyl, etc.; R4 represents a —C1-6 alkyl, etc.; X5 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].