Provided is a device for preventing eavesdropping through a speaker. More particularly, a device for preventing eavesdropping by transmitting a jamming signal through a speaker common signal line is provided, the device including: a jamming signal generator for generating a jamming signal comprising a noise signal; an amplifier for amplifying the jamming signal; and a transformer for receiving the amplified jamming signal from the amplifier and outputting the amplified jamming signal to a speaker common signal line. The device may transmit a jamming signal in an audible frequency band to the speaker common signal line, thereby rendering conversations unrecognizable to eavesdroppers when an electrical signal induced from a speaker is detected through the speaker common signal line.