A safety output includes an output controller to make an instruction to output normal output data and first self-diagnosis pattern data synchronously with a control cycle, a normal output unit to output the normal output data synchronously with the control cycle, a test pattern generating unit to encode the self-diagnosis pattern data into a pulse train signal having a pulse width not larger than a preset value and output the pulse train signal in accordance with a baseband transmission system, a combination output unit to combine the pulse train signal with the normal output signal and output the resultant signal, a reconfiguration unit to decode the inputted operation-terminal-portion output signal to reconfigure the operation-terminal-portion output signal as second self-diagnosis pattern data, and a comparator to compare the first self-diagnosis pattern data with the second self-diagnosis pattern data to judge the presence or absence of a difference.