PURPOSE: To prevent an output sound from being excessively outputted by controlling a compression corresponding to an inputted audio signal so as to control an output sound volume within a prescribed range thereby compressing the dynamic range in response to a sound volume set by the user.

CONSTITUTION: A ratio of an input level to an output level is set in a form of a nonlinear mode curve, and a sound volume is compressed in such a way that in the case of a small level input, for example, in the curve A, a gradient Q1 is set larger and in the case of a large level input in the curve A, a gradient Q2 is set smaller. In order to attain the compression mode, for example, several kinds of nonlinear mode curves A-C are stored in the inside of a sound signal processing section 5 as a ROM table, one curve with gradient A-C is selected from the table based on a set input by the volume operation of the user to control the output level with respect to the input level.