Safety device and safety method

A safety device comprising:

• a plurality of arithmetic units which operate in an asynchronous manner relative to each other and each configured to output an arithmetic result of input data as arithmetic data in each control period;
• a first comparison unit configured to compare information indicating the control period at a timing at which each of the plurality of arithmetic units outputs the arithmetic data;
• a plurality of temporary storage units configured to hold the arithmetic data output by the plurality of arithmetic units, respectively;
• a second comparison unit configured to compare the arithmetic data held by the plurality of temporary storage units;
• and
• an output unit configured to output the arithmetic data to outside, wherein
• each of the plurality of temporary storage units outputs the arithmetic data held therein according to a comparison result from the first comparison unit,
• the output unit outputs the arithmetic data output by the temporary storage units to the outside when a comparison result from the second comparison unit indicates a match, and stops outputting the arithmetic data to the outside when the comparison result from the second comparison unit indicates a mismatch, and
• the second comparison unit maintains the mismatch even when the comparison result from the second comparison unit changes to indicate a match in control periods after a time point of the mismatch.