A hinge mechanism is provided, including a fixed member, a rotary member pivotally connected to the fixed member, a pin, a first gear set, and a second gear set. The first and second gear sets are connected to the fixed member and the rod and respectively have a teeth-uncompleted gear. When the rotary member rotates relative to the fixed member from an initial angle to a first angle, the first gear set drives the pin to rotate in a first direction. When the rotary member further rotates relative to the fixed member from the first angle to a second angle, the second gear set drives the ping to rotate in a second direction, which is the opposite of the first direction.