A keyboard apparatus is provided with a key unit that has a plurality of keys supported for pivotal motion. Also provided is a detection section for detecting a key speed when any of the keys are pivoted. The key unit and detection section are supported by a housing having a bottom member formed of a resin. A reinforcing member having a sufficient rigidity is provided to reinforce the bottom member of the housing such as to reduce warping of the bottom member so as to reduce movement of the detection section as a result of warping of the bottom member.