A surveillance camera system includes a multiplexer. The multiplexer successively selects image data output from each surveillance camera one by one so as to input the selected image data to an image recording apparatus. The image data input to the image recording apparatus is subjected to a compression process by a compression expansion circuit and then, recorded on a hard disk. The compression process is performed on the basis of a reference coefficient stored in a management list within a memory. It is noted that a value capable of the image data to be compressed up to a size within a target range is set as a reference coefficient in an initialization process by a CPU. Furthermore, the reference coefficient is sequentially renewed by the CPU at a recording process.