A hinge mechanism includes a shaft, a cam, a spring and a sliding member. The shaft has a first end and a second end and the cam is movably disposed at the first end and has an inclined plane facing the second end. Also, the spring is disposed at the second end, and the sliding member is disposed on the shaft and is coupled with the spring. The sliding member moves along the shaft due to the elasticity of the spring. In addition, the sliding member has a contact capable of reaching the inclined plane, wherein the cam on which a force is imposed moves toward the second end so that an elastic potential energy is stored as a result of elastic deformation of the spring and the contact of the sliding member presses the inclined plane to rotate the cam by the spring's resilience.