A bridge expansion joint comprising: a pair of lower plates being disposed between one bridge deck section and the other bridge deck section with leaving a predetermined interval; an upper plate being respectively disposed on an upper surface of the lower plate, in which the width of the upper plate in the horizontal direction is smaller than that of the lower plate; and a load supporting means being disposed on the upper surface of the upper plate, the load supporting means comprising a pair of link members (400, 400a) or a pair of finger members, characterized by the bridge expansion joint further comprising: a reinforced plate being disposed between the load supporting means and the lower plate, in which an inclined plane is respectively provided at both sides of the reinforced plate so that the reinforced plate has a narrow top and wide bottom-shaped section; wherein a storage space is defined by a lower surface of the load supporting means, the upper surface of the lower plate, the inclined planes of the reinforced plate, and the side surface of the upper plate; and wherein a plurality of penetration-prevention grooves are formed at the lower surface of the reinforced plate in such a manner that they extend along the longitudinal direction of the reinforced plate and they are spaced equally with each other along the width direction of the reinforced plate so as to restrain the flow of infiltrating water through a gap provided between the lower surface of the reinforced plate and the upper surface of the lower plate. a pair of lower plates being disposed between one bridge deck section and the other bridge deck section with leaving a predetermined interval; an upper plate being respectively disposed on an upper surface of the lower plate, in which the width of the upper plate in the horizontal direction is smaller than that of the lower plate; and a load supporting means being disposed on the upper surface of the upper plate, the load supporting means comprising a pair of link members (400, 400a) or a pair of finger members, characterized by the bridge expansion joint further comprising: a reinforced plate being disposed between the load supporting means and the lower plate, in which an inclined plane is respectively provided at both sides of the reinforced plate so that the reinforced plate has a narrow top and wide bottom-shaped section; wherein a storage space is defined by a lower surface of the load supporting means, the upper surface of the lower plate, the inclined planes of the reinforced plate, and the side surface of the upper plate; and wherein a plurality of penetration-prevention grooves are formed at the lower surface of the reinforced plate in such a manner that they extend along the longitudinal direction of the reinforced plate and they are spaced equally with each other along the width direction of the reinforced plate so as to restrain the flow of infiltrating water through a gap provided between the lower surface of the reinforced plate and the upper surface of the lower plate. a reinforced plate being disposed between the load supporting means and the lower plate, in which an inclined plane is respectively provided at both sides of the reinforced plate so that the reinforced plate has a narrow top and wide bottom-shaped section; wherein a storage space is defined by a lower surface of the load supporting means, the upper surface of the lower plate, the inclined planes of the reinforced plate, and the side surface of the upper plate; and wherein a plurality of penetration-prevention grooves are formed at the lower surface of the reinforced plate in such a manner that they extend along the longitudinal direction of the reinforced plate and they are spaced equally with each other along the width direction of the reinforced plate so as to restrain the flow of infiltrating water through a gap provided between the lower surface of the reinforced plate and the upper surface of the lower plate.