A management processor (32) of a main processor unit (100) transmits a request for task switching that includes information related to a task performed after the switching, from a main processor communication unit (62) to a graphic processor communication unit (72) of a graphic processor unit (100). A memory controller (70) of the graphic processor unit (100) reads image-related data related to a task before the change from a graphic memory (10), and saves the read data in a main memory (50). The memory controller (70) reads the data related to the task after the change from the main memory (50), which stores previously saved image-related data. The memory controller (70) restores the read data to the graphic memory (10). The graphic processor communication unit (72) transmits an acceptance permit signal indicating that the graphic processor unit (100) is ready for task switching to the main processor communication unit (62). After acknowledging the acceptance permit signal, the main processor unit (200) switches between tasks in the management processor (32).