The present invention discloses an enclosed hinge device with a readily center-aligned mechanism, employing two protruded blocks of a locking retainer engaged into and fastened with two notch grooves of an arresting part to form two positioning points, such that the locking retainer and the arresting part are not slidable therebetween along with the advantage of easy assembly. Further, the securingly connection between the enclosing part, the arresting part, and the locking retainer also enhances the structural strength, thereby reducing the rotational shaking of the pivotal axle.