Provided is a loudspeaker device that includes a body and a lock lever. The body includes an actuator that operates in response to an input drive signal, and an attachment part attachable to an adapter mounted on a helmet and including an engagement part. The lock lever includes a locking part, the lock lever being rotatably supported by the body, and allow, when rotated, the locking part to be engaged with the engagement part. The loudspeaker device is designed to be attachable and detachable to and from the adapter. The body is designed to be locked on the adapter, as a result of engagement of the locking part with the engagement part. The loudspeaker device allows for easy mounting on the helmet, while being prevented in a mounted state from falling from the helmet.