An apparatus for detecting the position of the paintball of a paintball gun includes an induction plate responsive to electrostatic capacity. The induction plate is positioned at a corresponding side of the ball-falling tube within the firing area of the gun barrel, and the induction plate consists of a conductive terminal piece and equivalent electrostatic capacity. An insulated body is interposed between the terminal piece and the gun barrel. Besides, an electrostatic capacity detection circuit is electrically coupled to the induction plate for detecting the change of the electrostatic capacity of the induction plate. Moreover, the signal of the change of the electrostatic capacity is transmitted to the paintball-firing circuit for a reliable detection if the paintball accurately reaches the firing area such that the push tube may be actuated in accordance with this information. In this way, an accurate detection is ensured without being disturbed by other light sources. Moreover, an undesired firing action is avoided when the paintball is still not fed in position. In addition, it is not required to clean up the firing area. Furthermore, a low power consumption is achieved.