To provide a computer capable of performing screen capturing without applying any burden onto a CPU.

Each time a display image is modified wholly or partially periodically during display of a learning screen, a CPU 2A sends an instruction for compressing image data of a display screen to a GPU 12A of a graphic board 8A and in parallel with image generation, on the basis of an image compression program, the instructed GPU 12A compresses image data of the display screen stored in an image storage region of a video memory 11A in accordance with a still picture format of JPEG or the like, stores the image data in a work region of the video memory 11A, reads out the compressed image data and temporarily stores the compressed image data in a main memory 3 via a PCI bus 4. Each time new compressed image data are stored in the main memory 3, the CPU 2A reads and outputs the compressed image data to a network board 10 and sends them to an external teacher terminal computer via a local network or public network through network communication.