To provide a process input/output device which can switch its output to the most suitable value instantaneously in the case of a power failure, at the time of recovery, or in interlock condition operation.

In the process input/output device, an information storage circuit 4 is incorporated which stores output information corresponding to various factors. Information fetched by a monitor controller interface circuit 1 is normally outputted from an output circuit 3. In case of a power failure, at the time of recovery, or if each interlock factor operates, a factor input circuit 5 takes output information corresponding to a factor inputted from the information storage circuit 4 and it is selected by an output selecting circuit 2 and outputted from the output circuit 3. Consequently, the output can instantaneously be switched to the most suitable value.