"Specification for the design of crane structures" was issued in 1976 as JIS B8821. Since then, fatigue life of cranes has been designed as 2×(10)^6 cycles. Recently, some cranes have been used beyond the designed operation ratio because of demands of increasing transportation quantities. More long fatigue life has been cried for crane structures. Therefore, amendment for the specification has been carried out. In the revised specification, fatigue design curves of welding joints subjected to normal stress are composed of 15 curves depending on strength category of the joints, and the fatigue lives are covered in the range from (10)^4 to (10)^8 cycles. Fatigue strength under variable amplitude stresses can be evaluated based on the linear damage rule. Fatigue assessment can be carried out by using design stress, allowable stress and safety factors.