To provide a method and device that can evaluate the delay destructiveness of a steel material under slight hydrogen penetration conditions and a measuring method that can easily measure a slight amount of penetrating hydrogen.

A rod steel material having a circumferential cut is fatigued and the frequency up to its fatigue destruction is found to evaluate its delay destructiveness. At this time, a static bending load is placed on the steel material for a certain fixed time to give bending fatigue and break it, and when the delay destructiveness is evaluated, the amount of hydrogen penetrating the steel material is measured. In this case, the steel material is subjected to a hydrogen penetrating process, the frequency of the fatigue destruction of the steel material is measured by applying this evaluating method, and another steel material in a similar shape is subjected to bending fatiguing to measure the frequency of fatigue destruction, thereby contrasting the frequencies of fatigue destruction with each other. The evaluating device is equipped with a 1st grip member 20 which holds one end of the test-piece 10, a 2nd grip member 22 which holds the other end, and a rotary shaft 30. A lever 40 is coupled with the 2nd grip member through a coupling 52.