The research works for the Weibull distribution function proposed by Weibull in 1939 and for the dynamic capacity and life formula of rolling bearings postulated by Lundberg and Palmgren in 1947 were revisited and reexamined especially material function and P-S-N (Probabilistic Stress-Life) relation in structural materials as well as P-F-L (Probabilistic Force-Life) relation in rolling bearings. By using the three-parameter Weibull distribution function introduced a minimum strength/life as a third parameter, a new statistical theory for treating the static/dynamic strength of materials and P-F-L test of rolling bearings were developed. As a result, the stressed volume for materials in equi-stressed field yields to a stressed volume, area, length and/or points concerning a critical stress of failure depending on acting loads, because they express the number of probability products. It was developed that a 50% rating stress for static strength and a 90% rating stress for dynamic strength of materials as well as 90% rating load for rolling bearings were specified. Further it was found that a stress-life/load-life exponent which depends on the strength of materials/bearings was independent from the Weibull slope as well as a stressed volume.