To respond to an n-bit digital signal, a speaker (1) is provided that includes an sound pressure generator (10) including 2i−1 piezoelectric elements (51, 52, and 53) for an i-th bit, and a total of 2n−1 stacked piezoelectric elements (51, 52, and 53). Due to divided vibration of the piezoelectric elements (51, 52, and 53), the speaker (1) has low directionality. Planar electrodes (80, 81, 82, and 83), to which voltage is applied, are provided between the piezoelectric elements (51, 52, and 53). By this means, all the piezoelectric elements can be driven using similar voltages, and high sound quality can be obtained without a problem of unit-to-unit differences between voltage sources.