Self-loosening of threaded fasteners sometimes occurs under dynamic loads such as vibration and shock. For mechanical structures, the self-loosening of threaded fasteners under transversely repeated load is particularly important. Although many parts for preventing the loosening of the bolt joints are evaluated the locking performance of selfloosening, there are not clear about the locking performance of the spring washer. The spring washers are used in many mechanical structures, so that in order to improve the reliability of the bolt joints, it is required to verify the effectiveness about the bolt loosening using the spring washer. In this paper, we clarified the effectiveness of the spring washer about the bolt loosening from the experimental evaluation of the bolt joints using the spring washer under the transverse vibration, and proposed the design guideline to adopt the spring washer based on the result. In the fastening using the spring washer, the lubrication state of the bearing surface and the mounting direction of the spring washer influence the self-loosening with rotation of the bolt joints under the transverse vibration. In order to prevent the self-loosening of the bolt joints using a spring washer, it is necessary to satisfy the condition that the fastening surface does not slip. And the spring washer functions effectively as the bolt tension compensation only when the residual bolt tension is smaller than the contact load of the spring washer.