PURPOSE: To shorten the stop time of online operation and to stabilize the operation of a CPU, by changing the set value of the normal completion monitoring time in an emergency operation controller to a short-time value when the program of the CPU is not executed owing to a power failure, etc.

CONSTITUTION: Two CPUs 20 and 21 are operated in dual mode to constitute a data processing system, which is provided with one emergency operation controller 1. This controller 1 is provided with fault detecting circuits 30 and 31 which detect faults of the CPUs 20 and 21, an indicating circuit 5 which sends an operation indication to the CPUs 20 and 21, and a status bit 4 for deciding on which CPU20 or 21 the indication is sent to. Further, a monitoring timer 6 for monitoring normal completion and detecting circuits 70 and 71 which detect the operation failure of a microprogram due to a power failure and a clock break of the CPUs 20 and 21 are provided. When the circuits 70 and 71 detect the operation failure conditions of the CPUs 20 and 21, the set time of the timer 6 is shortened.