In accordance with a kind of effect, an effect adding section (38) adds an original microphone signal with an effect signal and outputs the added signal, or outputs an effect signal in place of the original microphone signal. A mixing section (42) mixes the effect signal and the original microphone signal at a variable mixing ratio. The mixed signal is supplied to an echo signal generating circuit (20) to generate an echo signal. An output signal of the effect adding section (38) and the echo signal output from an echo adding section (40) are mixed by a mixing circuit (18). In the case in which both an effect and an echo are added such that the microphone signal and the effect signal are added and then output, the mixing section (42) reduces the mixing ratio of the effect signal, whereby the effect is prevented from being excessively increased.