A safety device comprises a first computation unit, a second computation unit, an output control unit, and a first central computation processing unit, further comprising the first computation unit and the second computation unit. The first computation unit and the second computation unit are different hardware. The first computation unit carries out a first computation on a detected value which is detected from a control object and acquires a first result value. The second computation unit carries out a second computation on the detected value, acquires a second result value, and assesses whether the first result value and the second result value match. If the second computation unit assesses that the first result value and the second result value match, the output control unit outputs the first result value. If the second computation unit assesses that the first result value and the second result value do not match, the second computation unit does not output the first result value.