Abstract: A buckle apparatus for use in a seatbelt system is arranged such that when the tongue plate of the seatbelt is inserted into the buckle body, the pawl of a lock plate is inserted into an opening formed in the tongue plate. Since the projecting end of the pawl is separated from the corresponding opening formed in the buckle body, a relatively small force can release the tongue plate from the buckle apparatus. However, when the force applied to the tongue plate for pulling it out from the buckle apparatus increases, a lock plate holder is deformed by virtue of this force. In consequence, the pawl engages with the opening of the buckle body, and retaining wings provided on the side of the lock plate remote from the pawl also engage with the corresponding portions of the buckle body. Accordingly, the lock plate is supported by the buckle body at two portions on both sides of the portion thereof which engages with the tongue plate, so that the lock plate can bear a large tongue plate pulling out force.