The Coulomb's Failure Criterion for materials is commonly and implicitly applied to the stress components on failure plane. In this paper, it was attempted to apply the Coulomb's Criterion not only to the failure plane but also to general planes which have various directions relative to the principal stress components at failure conditions, and it was shown that the previously proposed well-known criteria for materials could be expressed by an unified simple equation. This fact indicates that the direction of the plane for the Coulomb's Criterion is a material property as well as the friction ratio and cohesion. The revised Coulomb's Criterion was applied to simulate test results, and it was shown that the model could reproduce the test data fittingly.