The present invention provides a planer acoustic transducer including a vibrating diaphragm including a spiral voice coil provided on both surfaces or on one surface of an insulating base film; and a permanent magnet corresponding to the voice coil, wherein, in the vibrating diaphragm, the spiral voice coil is formed by applying a wire conductor, in a coil pattern, onto a sheet-like substrate having an adhesive layer on at least one surface thereof. Alternatively, at least a portion of the vibrating diaphragm, which portion corresponds to the loop of a first or second vibration mode, is reinforced with a rigidity-imparting member; the substrate of the vibrating diaphragm is formed of a resin foam; or the voice coil is formed three-dimensionally.