1. A central processor of a programmable logic controller (PLC) for controlling an object of control, the central processor being configured to control the object by repeating transmission of output data, reception of input data and execution of a control program producing the output data using the input data, comprising: a storage that stores a system program and the control program; and a microprocessor that executes the control program and the system program; a communication circuit that transmits the output data and receives the input data, wherein the system program comprising, as an execution preparation process for controlling the PLC: a process for producing a reception buffer that stores the received input data in the storage, and a process for producing, for each of the input data referred to by the control program, an input synchronization buffer used by the control program as a reference target for the input data; and the system program further comprising, as an execution control process for the controlling the PLC, an input copy process for copying the received input data from the reception buffer to the input synchronization buffer corresponding to the input data, and a control program start process for starting an execution of the control program.