This invention intends to provide a speaker which assumes a comparatively large area in a device without spoiling various display effects. The transparent flat panel speaker of this invention is a speaker of high efficiency which can give forth a sound volume large considering the small-sized device even when driven by a low voltage.The transparent flat panel speaker of this invention comprises, at least, a transparent resonator plate and a plate of a piezoelectric material held between at least one pair of electrodes, the resonator being excited by the piezoelectric material plate, a periphery of the resonator plate having a shape which is represented by a curve or in which straight lines are connected by smooth curves with at least two centers of curvature.As the peripheral shapes, an ellipse, a curve expressed by X.sup.n /a+Y.sup.n /b=1, a plane figure obtained by molding the corners of a polygon circumscribed or inscribed to an ellipse, etc. are especially favorable for the speaker.