In bolted joints, severe accidents caused by self-loosening frequently occur. The decrease tendency of the initial clamping force (axial tension) is thought to be the loosening phenomenon. For judgment of the self-loosening, the relative evaluation of locking device/method is performed by using Junker’s style loosening test equipment, for example. However, our basic question is "For how many tens of thousands of miles (operations), does the locking device maintain the clamping force before becoming loose?" This absolute evaluation on self-loosening is indispensable for the prediction of the lifetime to loosening failure and for the development of the product. From the author’s previous paper, there is a good linear relation on logarithmic coordinates between the decrease of clamping force ratio (measured /initial clamping force) and number of operations (or mileage or working time) since the last tightening. In this paper, observation results of loosening phenomenon in industrial vehicle (large sized forklift-truck) are analyzed for this linear relation by the proposed regression formula. Based on the relation, in early stages of the development test of the actual machine, the rate of clamping force decrease can be estimated accurately after prolonged operation since the initial tightening by measuring the initial clamping force behavior. The tendency to decrease is observed about the depression type (static) and working load type loosening (dynamic). For evaluation design bases, the residual clamping force estimation chart is established. On the other hand, the L-N (Loosening Lifetime - Number of Cycles to Loosening N) diagram is proposed for the loosening lifetime prediction of working load type loosening also. Using the loosening damage (cumulative decrease of clamping force) and L-N diagram, the lifetime to loosening failure can be predicted accurately for the locking device/method as an absolute evaluation.