The present invention relates to a compound which has a glucokinase-activating effect and is useful as a therapeutic agent for diabetes mellitus, being represented by a formula (I): ##STR00001## [wherein X.sup.1 represents a nitrogen atom, sulfur atom, oxygen atom or the like; R.sup.1 represents a 6- to 10-membered aryl group, 5- to 7-membered heteroaryl group or the like; D represents an oxygen atom or sulfur atom; R.sup.2 and R.sup.3 are the same or different, each representing a hydrogen atom, lower alkyl group or the like; a formula (II) ##STR00002## represents an optionally substituted 5- to 7-membered heteroaryl group or the like; a formula (III) ##STR00003## represents a monocyclic or bicyclic heteroaryl group] or a pharmaceutically acceptable salt thereof.