To improve reproduction characteristics of a signal of small sound volume from a speaker.

In the case of characteristics, linearity of an output level to an input signal is almost secured when it is above a prescribed level and the output level to the input signal drops when it is below a prescribed level, as input/output characteristics of the connected speaker device. Correction processing for compensating a drop amount of the output level is executed to a signal component, which is below a prescribed level, of the inputted audio signal, and also, a gain for strengthening the signal component, which is almost below a prescribed level, at least at a low frequency is set higher than the other frequency bands by setting it to a gain of exceeding an amount for compensating the drop amount.