A keyboard device includes a plurality of transmission members which are displaced in response to a depression operation on each of a plurality of keys and a plurality of hammer members each of which provides an action load to a depressed key by performing a rotating motion in response to the displacement of a transmission member corresponding to the depressed key. The weight of the transmission member is set in accordance with the formation density of a plurality of ribs formed on a transmission body section. Therefore, the weight of the transmission member set in accordance with the formation density of the ribs can be provided to the key as a static load. As a result of this structure, an initial load on a key can be optimized, and a key depressing force on the key at the time of key depression can be favorably transmitted to the hammer member.