PURPOSE: To ensure the stable and sure rise of an initial program loading IPL system by performing an IPL job after ready state signals received from each device are confirmed.

CONSTITUTION: Input/output controllers 3W5 connected with input/output devices 6W8 are connected to an interface bus 17 of a channel CH2 connected to a CPU 1. The controllers 3W5 contain means which set the states showing whether devices 6W8 are ready or not and send state signals 18W19 to the bus 17. The CPU 1 detects the state signals collected via the CH2 and starts an IPL action only when all state signals are set under ready states. Thus the stable and sure rise is secured with this system together with satisfactory operability and high reliability with no human error.