A data compression and decompression unit that can enhance a data throughput during compression and decompression of data by dynamically allocating the sizes of the input and output buffers to the compression and decompression sections in accordance with a compressibility of data. The data compression and decompression unit includes a compression section that receives bit map data from a terminal, compresses the bit map data with a predetermined compressibility, and generates compressed data, and a decompression section that decompresses the compressed data into an original format, and generates decompressed data. The data unit further includes a memory section that stores the bit map data, the compressed data, and the decompressed data, and a control section that controls the compression and decompression in accordance with the predetermined compressibility.