An adjustment device includes a base, a ratchet wheel assembly and a fixing rod. The base includes an accommodating groove and ratchet teeth. The ratchet wheel assembly is rotatably accommodated in the accommodating groove and includes a body, an elastic arm, and a pawl. The elastic arm includes a first connecting segment connected to the body and a second connecting segment connected to the pawl. The pawl may engage with one of the ratchet teeth. The fixing rod movably extends between the body and the elastic arm. When the fixing rod is arranged between the second connecting segment and the body, the pawl is fixed to the ratchet teeth, so that the ratchet wheel assembly is positioned on the base. When the fixing rod is arranged between the first connecting segment and the body, the ratchet wheel assembly may rotate relative to the base.