PURPOSE: To obtain precise information enough for investigating the cause of time-out by sampling log-out information at a log means provided in the constitutive element of a system generating a fault.

CONSTITUTION: When the time-out of an input/output device 4 is detected, an operating system (managing means 21) transmits a log-out activating instruction from an instruction processor 1 to an input/output channel device 3. The input/ output channel device 3 (log means 22) samples input/output state information 9 from the hardware inside of the input/output channel device 3, temporarily stores the information in a log buffer 8 of the above device and transmits a recording end to the instruction processor 1. Afterwards, the contents of the log buffer 8 are recorded in a disk device 7 of a service processor 6 by an extracting means 23 asynchronously with the log-out activating instruction.