Abstract: A seismic reinforcement device for a bridge includes a first member having a projecting portion and a second member having a depressed portion. The device has a horizontal force sharing function in which the projecting and the depressed portions are freely fitted to and engaged with one another to constitute a shear key and resist a horizontal force by causing the first member to be coupled to and supported by any one of the substructure and the superstructure and causing the second member to be coupled to and supported by the other of the substructure and the superstructure. In addition, the device has a level difference preventive function that suppresses dropping of the superstructure and reduces a level difference of the substructure and the superstructure by interposing a spacer having a predetermined thickness between the first and second members or between the substructure or the superstructure and the device.