An image signal processing apparatus includes two JPEG codecs. A plurality of frames of image signals periodically input from a multiplexer are individually compressed by the two JPEG codecs, and the compressed image signals are recorded on a hard disk by an HDD. Furthermore, the plurality of frames of the compressed image signals reproduced from the hard disk are individually expanded by the two JPEG codecs, and the expanded image signals are output to a monitor. Herein, each of the JPEG codecs selectively executes individual compression of the plurality of frames of the image signals and individual expansion of the plurality of frames of the compressed image signals. A CPU makes the JPEG codecs perform the compression process prior to the expansion process.