PROGRAM CODE CHANGING SYSTEM

PURPOSE:To simplify the whole changing work of a program code by providing a shared memory shared by plural controllers for constituting a group, and executing the revising operation of a microprogram at every controller group. CONSTITUTION:In a shared memory 107, program change data 113, a first flag 108 for showing a fact that one of plural controllers 103 - 106 belonging to one group is performing the revising operation of a microprogram, second flags 109 - 112 for showing a fact that the revising operation of the microprogram allocated to each controller 103 - 106 is completed or not completed yet, and a third flag 107a by which each controller 103 - 106 executes exclusively an access to the shared memory 107 are stored. In this state, the revising operation of the microprogram is executed at every controller 103 - 106 group.