A topboard reflection preventer for a grand piano, which is capable of positively preventing lighting from being reflected by an open topboard, while maintaining excellent appearance of a piano body. The topboard reflection preventer for a grand piano is attached to an openable and closable topboard formed by a topboard rear and a topboard front, and prevents lighting from above from being reflected by the topboard in a state of the topboard held open in an inclined position. The topboard reflection preventer includes a reflection preventer body attached to the topboard rear and the topboard front folded onto the topboard rear, in a state covering whole upper surfaces of the topboard rear and the topboard front, and a holding member for holding the reflection preventer body so as to prevent the reflection preventer body from falling off the topboard held open in the inclined position.