A speaker driving device applies a constant voltage of a constant voltage source (3) a pair of voice coils (5) alternatively by switching the direction of applying the constant voltage based on a binary PDM signal. A AE modulator (2) produces the binary PDM signal by △∑ - modulating a digital audio signal from a digital low - pass filter (1). The constant volt - age is applied to a first voice coil in one direction and is applied to a second voice coil in the reverse direction by switching (4) the direction of applying the constant voltage. The first and second voice coils forms the pair of voice coils. This arrangement causes a current to flow through the first and second voice coils in opposite directions and a diaphragm of a speaker to be driven in two directions opposite to each other. As a result, the speaker is driven more efficiently. Moreover, since the switching of the di - rection of applying the constant voltage is performed by changing the connections between the constant voltage source and the pair of voice coils, a switch - ing circuit (4) with a simplified structure is used.