A first magnet is provided in an upper case and a second magnet is provided in a lower case so that these magnets face each other. These magnets are magnetized in opposite directions. A diaphragm having a drive coil is placed between these magnets. Thus, magnetic flux emitted from the respective magnets bends in a direction approximately perpendicular to the initial direction of emission of the flux. In the magnetic field, the component of the magnetic flux in the direction of radiation proportional to the driving force is dominant, and is symmetrical relative to the direction of vibration. Therefore, the sound pressure of the reproduced sound is increased and the secondary harmonic distortion caused by asymmetry of the driving force can be reduced.