A data compression apparatus includes a characterizing point extracting part which extracts data expressing characterizing points included in a plurality of data showing a result of carrying out simulation a quantized data generating part which generates quantized data obtained by quantizing data except for data expressing characterizing points, and a file number converting part which converts the same types of quantized data including in the quantized data, into a relating file number. During data compression, data except for the characterizing points is compressed. If the same quantized data is included at the same address location in the previously-compressed file, the quantized data is replaced with the file number of the previous compression file, thereby compressing data at high efficiency.