This invention provides a process control simulator configured to efficiently debug a plant control system. A computer stores simulated data generated by a model executing part to a time-series memory area. A programmable controller stops input from the input-device interface when there is a virtual input/output request received. A virtual input/output processor sets simulated data from a time-series memory area of the computer to a time-series memory area of the programmable controller. A program executing part sets simulated data from the time-series memory area to a memory area at the same resolution as an arithmetic operation period of program execution and executes the program. Control output as a result of the execution is fed back to the model executing part of the computer, and the computer calculates simulated data as process value at this timing, and stores the data to its time-series memory area.