Disclosed is a buckle apparatus for a seat belt. The buckle apparatus Includes an upper cover including a front plate formed with an opening part; a lower cover engaged with a lower portion of the upper cover and provided therein with a base frame; a latch member including one end rotatably supported on the base frame and locked with a tongue plate inserted through the opening part; an ejector assembly provided on the base frame for locking and releasing between the tongue plate and the latch member; and a release button slidably provided on both sides of the base frame and disposed in an upper portion of the opening part so that one side of the release button is exposed. At least one elastic member is integrally provided on an upper end of the front plate to elastically press a bottom surface of the tongue plate.