To eliminate a troublesome replacing work by writing the contents memorized in a memory simply into the memory of an other control device of the same kind, when a control device is replaced due to its failure.

A control device A is provided with a communication device 5 having input/output terminals 6 for communicating with an other control device B of the same kind and a writing means for writing the contents memorized in the memory 4 of the control device A into the memory 14 of the other control device B of the same kind while connecting the input/output terminals 6, 16 each other communicatingly with the other control device B of the same kind or a read-in means for reading the contents memorized in the memory 14 of the other control device B of the same kind into the memory 4 of the control device A.