A keyboard instrument which is capable of ensuring sufficient strength of neighboring portions of chassis and preventing generation of noise, while restricting lateral motion of hammers. Keys are pivotally supported by chassis arranged side by side in a left-right direction. Hammers are pivotally supported by the chassis, for each being pivotally moved in accordance with depression of the associated key. Guides are formed in the chassis and each have a pair of left and right sidewalls opposed to the associated hammer from opposite sides, for restricting lateral motion of the associated hammer. Out of the guides, one at a boundary of each adjacent two of the chassis has the pair of sidewalls formed by an end sidewall of one of the adjacent two chassis and an end sidewall of the other of the same.