Positive and negative two terminals of each of a plurality of main speakers constituting an array speaker are connected to each of amplifiers. Then, the main speakers are bridge-driven. Sub-speakers interpolating the main speakers are arranged respectively between the main speakers. Then, the positive and negative terminals of each of the sub-speakers are connected respectively to the terminals of the same polarities of the adjacent two of the main speakers. One sub-speaker receives an average value of the signals provided to the adjacent two main speakers, so that the one sub-speaker interpolates the wavefronts emitted from the adjacent two main speakers.