PURPOSE: To provide the shared system of a remote I/O slave station unit by plural masters PC without generating a failure such as congestion, in the data input/output between the masters PC by performing an exclusive input/output control for the shared slave between the plural masters PC.

CONSTITUTION: This system is the remote I/O transmission system of a programmable controller where plural programmable controller main bodies 1 having remote I/O master station units 11, respectively, is provided and a remote I/O slave station unit that these plural programmable controller main bodies 1 share with each other for data input/output is included. Each programmable controller main body 1 has a memory storing a flag for performing an exclusive input/output control for the remote I/O slave station unit in the rewritable area of the memory and an exclusive input/ output control part performing the exclusive input/output control for the remote I/O slave station unit in accordance with the flag stored in the memory.