A hinge mechanism includes a connecting member, two pivotal shafts substantially parallel to each other, two main gears, two transmission gears, and a resisting member. The connecting member sleeves on the two pivotal shafts. The two main gears non-rotatably sleeve on the corresponding two pivotal shafts, respectively. The two transmission gears are rotatably positioned between the two main gears and mesh with each other and the two main gears. The resisting member sleeves on the two main pivotal shafts and holds the two main gears and the two transmission gears together with the connecting member.