PURPOSE: To simplify an application program by executing an error processing or a retry processing or the like for each I/O equipment asynchronously with a request from an application program by a device driver.

CONSTITUTION: The error processing or the retry processing or the like for each I/O equipment is preliminarily stored in the storage part of each device driver of an RAM 4 constituting a processing routine storage means. In this state, a central processing unit(CPU) 7 executes the application program in the control of the operating system of a single task and the device driver is operated by the request from the program. At this time, the leading address of a desired processing routine and desired time data are registered by a data registering means. Then, the execution of the application program is temporarily interrupted after the lapse of a time equivalent to the time data, the corresponding leading address is called and the pertinent processing routine is executed.