A digital camera includes a shutter button. An optimal compression ratio of an image signal fetched in response to a photographing instruction from the shutter button is predicted prior to the photographing instruction. More specifically, an image signal fetched before application of the photographing instruction is compressed by a JPEG codec, and the optimal compression ratio is predicted based on a size of a compressed image signal thus obtained. An image signal fetched in response to the photographing instruction is compressed on the basis of the optimal compression ratio, and a compressed image signal thus obtained is recorded onto a recording medium.