A safety control unit comprising: a memory configured to store a system program for safety control, a control program for safety control, and control data; a computation control part configured to execute safety control using the control data, the system program, and the control program; and an input and output unit for connecting the computation control part to a safety input device and to an output device, the safety input device being a device for providing safety control data via the input and output unit and the output device being a device to be safely controlled via the input and output unit which is configured to execute operations regarding safety control, wherein, the system program includes a data refresh program for executing a data refresh of safety control data in the control data of the memory received from the safety input device via the input and output unit and for accordingly outputting output data for safety control to the output device via the input and output unit, and the computation control part is configured to: receive a download instruction; continuously execute the system program and the control program while referring to the control data while the computational control part does not receive the download instruction; refer to the download instruction and detect whether to change the control program; stop executing the control program, if the computation control part receives a change of the control program which is not related to safety control, execute the change of the control program while executing a part of the system program including the data refresh program, and resume executing the control program, wherein the computation control part is configured to stop the data refresh program if the change of the control program is related to safety control. a memory configured to store a system program for safety control, a control program for safety control, and control data; a computation control part configured to execute safety control using the control data, the system program, and the control program; and an input and output unit for connecting the computation control part to a safety input device and to an output device, the safety input device being a device for providing safety control data via the input and output unit and the output device being a device to be safely controlled via the input and output unit which is configured to execute operations regarding safety control, wherein, the system program includes a data refresh program for executing a data refresh of safety control data in the control data of the memory received from the safety input device via the input and output unit and for accordingly outputting output data for safety control to the output device via the input and output unit, and the computation control part is configured to: receive a download instruction; continuously execute the system program and the control program while referring to the control data while the computational control part does not receive the download instruction; refer to the download instruction and detect whether to change the control program; stop executing the control program, if the computation control part receives a change of the control program which is not related to safety control, execute the change of the control program while executing a part of the system program including the data refresh program, and resume executing the control program, wherein the computation control part is configured to stop the data refresh program if the change of the control program is related to safety control. receive a download instruction; continuously execute the system program and the control program while referring to the control data while the computational control part does not receive the download instruction; refer to the download instruction and detect whether to change the control program; stop executing the control program, if the computation control part receives a change of the control program which is not related to safety control, execute the change of the control program while executing a part of the system program including the data refresh program, and resume executing the control program, wherein the computation control part is configured to stop the data refresh program if the change of the control program is related to safety control.