Provided is an electronic keyboard instrument and sound releasing method thereof. The electronic keyboard instrument includes: a plurality of keys, a housing that supports the plurality of keys, and one or more speakers arranged in the housing. At least one of the speakers is configured as a flat-plate speaker that includes a vibrating membrane on which a pattern of a conducting wire is formed and a pair of magnet plates disposed facing both surfaces of the vibrating membrane, and the flat-plate speaker vibrates the vibrating membrane with an electromagnetic force accompanying energization of the conducting wire.