A data processing apparatus includes an input portion, an output portion, a plurality of compressing/expanding devices which compress data-to-be-outputted inputted from the input portion and expand compressed data-to-be-outputted, a file memory which stores the data-to-be-outputted compressed by some or all of the plurality of compressing/expanding devices, a data discrimination portion which discriminates whether the data-to-be-outputted inputted from the input portion is data including a small amount of information or a large amount of information, and a transfer controller. In cases where it is discriminated by the data discrimination portion that the data-to-be-outputted is data including a small amount of information, the transfer controller transfers the data-to-be-outputted to the output portion through the plurality of compressing/expanding devices operating in parallel. In cases where it is discriminated by the data discrimination portion that the data-to-be-outputted is data including a large amount of information, the transfer controller transfers the data-to-be-outputted to some or all of the plurality of compressing/expanding devices while transferring the data-to-be-outputted to the output portion.