Cam adjustment device for lifting and lowering armrest and chair having the same

A cam adjustment device for lifting and lowering an armrest includes an armrest assembly and a support frame. The armrest assembly includes a connection base. The support frame has a support rod. The connection base is slidably connected to the support rod. A locking mechanism includes a cam wrench disposed on the connection base and rotatably installed on the connection base. The cam wrench is rotated such that a cam on the cam wrench presses and acts on the support rod. In a locked state, the cam wrench presses the support rod such that the connection base and the support rod are kept to be relatively fixed. In an unlocked state, the cam wrench is rotated to allow the cam to be released from the support rod, such that the connection base is lifted, lowered, and adjusted relative to the support rod.