PURPOSE: To unnecessitate the individual preservation and restoration of an environmental variable necessary after reponing a program on the side of a program by restoring the environmental variable saved and preserved in an environmental variable saving and preserving part.

CONSTITUTION: This computer system is provided with an operating system 2 executing a prescribed processing based on a program in a program preserving part 1. The computer system is provided with an environmental variable storage part 3 storing an enviromental variable specifying the execution environment of the program, a processing program storage part 4 storing plural kinds of processing programs, and a processing selection device 5 selecting a processing program based on the specified enviromental variable to make the operating system 2 execute. In addition, the computer system is provided with an environmental variable saving and preserving part 6 for saving and preserving the environmental variable, and environmental variable saving device 7 saving the environmental variable housed in the environmental variable storage part 3, and an environmental variable restoring device 8 restoring the saved and preserved environmental variable in the environmental variable storage part 3.