To allow an acoustic signal reproduced at a high speed to be processed in an excellent pitch transformation.

The time base compression acoustic signal reproduced at a high speed from a recording medium is processed by A/D conversion, and is written in a memory 10 to be accessed to in a toroidal state where the maximum and minimum values of the address value of the memory are continued. Reading digital data of an acoustic signal of which the pitch is converted in the state with the time base extended from memory 10 is successively carried out in a toroidal state where the maximum value and minimum values of the address value of the memory are continued. When the writing address value coincides with the reading address value, the data written in memory 10 is read and made to be data which is gradually reduced in the sound level, and the digital data of the acoustic signal from the above point in time is gradually increased in the acoustic level, and both data are synthesized and written in the memory 10 again.