A hinge mechanism includes a base, first, third, and fourth swing arms, a first support, first and second synchronous fitting members, an elastic member, and a cam member. The base is rotatably connected to the first swing arm. The first swing arm and the first support slide relative to each other. The third swing arm includes first and second arm bodies that are in sliding fit with the first support. The first and second synchronous fitting members are in linkage connection and are both movably mounted on the base. The first and second arm bodies are in transmission fit with the first synchronous fitting member. The fourth swing arm is in transmission fit with the second synchronous fitting member. The cam member and the base are relatively fastened. Two opposite ends of the elastic member respectively abut against the cam member and the base.