A duplexing process control device comprising a control system controller and a standby system controller, wherein the control system controller comprises: - a control data memory configured to store a control data, which is the data of the process state information for a predetermined program calculation for process control; - a control data collection control unit configured to store control data in a buffer memory while a control data collection flag is set; - a CPU configured to access an address in the control data in the control data memory when the CPU performs the predetermined program calculation; and configured to set the control data collection flag and clear the control data collection flag; wherein the control data collection control unit is configured to stop storing the address and the control data in the control data memory when the control data collection flag is cleared; wherein the control data collection control unit is configured to notify a control data transmission unit when the control data collection flag is cleared, and the buffer memory of the control system controller configured to store the address and the control data as an equalization data at the time of the predetermined program calculation of the CPU of the control system controller and - the control data transmission unit configured to sequentially read and transmit the equalization data from the buffer memory to the standby system controller when the data transmission notification is made, and wherein the standby system controller comprises: - a CPU of the standby system controller; - a buffer memory of the standby system controller configured to store the equalization data from the control transmission control unit, wherein the standby system controller is configured to expand the control data stored in the buffer memory of the standby system controller to the address transmitted from the control system controller before the predetermined program calculation of the CPU of the standby system controller is started, and wherein when the control system controller performs the predetermined program calculation, the address and the control data stored in the buffer memory of the control system controller are stored in the buffer memory of the standby system controller. - a control data memory configured to store a control data, which is the data of the process state information for a predetermined program calculation for process control; - a control data collection control unit configured to store control data in a buffer memory while a control data collection flag is set; - a CPU configured to access an address in the control data in the control data memory when the CPU performs the predetermined program calculation; and configured to set the control data collection flag and clear the control data collection flag; wherein the control data collection control unit is configured to stop storing the address and the control data in the control data memory when the control data collection flag is cleared; wherein the control data collection control unit is configured to notify a control data transmission unit when the control data collection flag is cleared, and the buffer memory of the control system controller configured to store the address and the control data as an equalization data at the time of the predetermined program calculation of the CPU of the control system controller and wherein the control data collection control unit is configured to stop storing the address and the control data in the control data memory when the control data collection flag is cleared; wherein the control data collection control unit is configured to notify a control data transmission unit when the control data collection flag is cleared, and the buffer memory of the control system controller configured to store the address and the control data as an equalization data at the time of the predetermined program calculation of the CPU of the control system controller and - the control data transmission unit configured to sequentially read and transmit the equalization data from the buffer memory to the standby system controller when the data transmission notification is made, and wherein the standby system controller comprises: - a CPU of the standby system controller; - a buffer memory of the standby system controller configured to store the equalization data from the control transmission control unit, wherein the standby system controller is configured to expand the control data stored in the buffer memory of the standby system controller to the address transmitted from the control system controller before the predetermined program calculation of the CPU of the standby system controller is started, and wherein when the control system controller performs the predetermined program calculation, the address and the control data stored in the buffer memory of the control system controller are stored in the buffer memory of the standby system controller.