In order to transfer at a high speed a large amount of data, such as data of a moving image, an image pickup system having an image pickup apparatus is arranged to convert an object image inputted through an optical system into an electrical signal, to convert the electrical signal into a digital signal by an A/D conversion part, to obtain from the digital signal a video signal in a predetermined form by a video signal generating part, to convert a color space of the video signal by a color space converting part in such a way as to compress the video signal according to a look-up table held within the color space converting part, and to transfer the compressed video signal to an external personal computer through an interface part.