Securing device for bicycle racks

A bicycle rack includes a main frame (20) connected to an upright post (100) and the ball (12) on the rod (11) connected to the vehicle is located between two side plates (22) and clamped by two clamping members (30,31). A pressing plate (50) has an upright plate (51) located between the two side plates (22) and a horizontal plate (52) which is connected to a holding member (60). A positioning bar (40) has a cam section (41) for pressing the pressing plate (50) to push one of the two clamping members (30,31) to clamp the ball (12). A U-shaped retaining member (70) is engaged with the rod (11) and is connected to the holding member (60) by using a U-shaped retaining piece (70). The ball (12) and the rod (11) are both secured so as to prevent the bicycle rack from shaking.