PURPOSE: To improve the continuousness and maintenance efficiency of an I/O control program part 2 by monitoring abnormality at the I/O of all peripheral devices around an information processor.

CONSTITUTION: When an I/O request is sent from an I/O control program part 2 to an abnormality monitoring part 4, a time-out time T for respective peripheral devices 6 is selected from a time table already storing the time-out time of respective peripheral devices 6 to start an I/O control device 3. An interval timer starting request is outputted to a timer device 5, and when either one, a time-out signal or an I/O end signal, is inputted after the end of I/O operation, whether the input signal is time-out or not is decided. When the decided result is 'YES', a time-out error is informed to the program part 2. In case of 'NO', the interval timer of the timer device 5 is cleared, the I/O end is informed to the program part 2 and control is transferred to the program part 2.