Large 3.5T-CT specimens were hydrogen charged in huge autoclave and crack growth tests were carried out in order to clarify the characteristics of hydrogen embrittlement due to absorbed hydrogen in steel. It was shown that absorbed hydrogen in the 3.5T-CT specimen remained for much longer period of time than 1.0T-CT specimen under exposure at room temperature air. The long-term tests developed under slow rising load reveals the fundamental crack growth characteristics. It was shown that when hydrogen is introduced in temper embrittled steel, the susceptibility to fast fracture significantly increases. K_<IC-H>; a stress intensity factor where crack growth rate shows rapid increase, was turned out to be lower than K_<IC>(H-free). Also, those temper + hydrogen effect at elevated temperatures are investigated.