A glucokinase activator is provided; and a treatment and/or a preventive for diabetes, or a treatment and/or a preventive for diabetes such as retinopathy, nephropathy, neurosis, ischemic cardiopathy, arteriosclerosis, and further a treatment and/or a preventive for obesity are provided.The invention relates to a compound of a formula (I): [wherein R1 and R2 represent a hydrogen, etc.; R3 represents a hydrogen atom, a halogen atom, etc.; R4 each independently represents a hydrogen atom, a lower alkyl group, etc.; Q represents a carbon atom, a nitrogen atom or a sulfur atom (the sulfur atom may be mono- or di-substituted with an oxo group); R5 and R6 each represent a hydrogen atom, a lower alkyl group, etc.; X1, X2, X3 and X4 each independently represent a carbon atom or a nitrogen atom; Z represents an oxygen atom, a sulfur atom or a nitrogen atom; Ar represents an aryl or heteroaryl group optionally mono to tri-substituted with a group selected from the substituent group β; ring A represents a 5- or 6-membered nitrogen-containing heteroaromatic group; m indicates an integer of from 1 to 6; n indicates an integer of from 0 to 3; p indicates an integer of from 0 to 2 (provided that at least two of X1 to X4 are carbon atoms); q indicates 0 or 1] or its pharmaceutically-acceptable salt, which has an effect of glucokinase activation and is useful as a treatment for diabetes.