A sound data processing apparatus includes a central processing unit for controlling predetermined processing in the apparatus, a rewritable RAM, a decoder performing the decoding processing for sound data, and an interface unit for being fitted with an external memory. The sound data processing apparatus reads a driver from the external memory mounted in the interface unit and stores the read driver into the RAM, and reads the sound data from the external memory with the driver and processes the read sound data. As a result, the wastefully using of the memory capacity of the memory mounted in the sound data processing apparatus is reduced.