A fallboard arrangement for a keyboard instrument, which makes it possible to make flat the entire upper surface of a keyboard instrument in a closed state. A fallboard back section is immovably provided in a rear part of the body, in a horizontal state. A fallboard is movable between a closed position where it is forward of the fallboard back section and has an upper surface thereof made flush with that of the fallboard back section in a state closing the performance section and an open position where it is upward of the fallboard back section so as to open the performance section. A hinge connects the fallboard to the fallboard back section in a manner pivotally movable between the closed position and the open position and is disposed downward of the fallboard in the closed position and the upper surface of the fallboard back section.