A head massager comprises a helmet having a front shell and a rear shell moveable relative to the front shell, a massage device and an adjustment device having a positive rotatable knob, a fixing pole fixed on the rear shell, a winding ring, two pulling ropes and a reverse locking device. The rear shell has a cavity and the front shell has two ends plug-connected with two ends of the rear shell. The knob and the winding ring are loosely sleeved on the fixing pole via holes. The knob has first bulged teeth around a hole, the winding ring has a loop of second bulged teeth around another hole. The first bulged teeth are indented joined to the second bulged teeth. One end of each pulling rope is connected to the end of the front shell, another end of the pulling rope is connected to the winding ring to rotate the knob in positive direction for moving the front shell by the two pulling ropes.