A staples push unit of a tacker includes a guide plate located at a staple outlet of the tacker. A motor is located in the tacker and has an output shaft to which a driving gear is connected. A slide and a push plate connected to the slide are movably located in a slot in the tacker. A rack is formed at one side of the slide and engaged with the teeth of the driving gear. A spring board has one end engaged with one end of the slide. When activating the motor, the driving gear drives the rack to move the slide, and the spring board is bent. When the teeth of the driving gear are disengaged from the rack, the spring board bounces back and drives the slide and the push plate to eject a staple. The push plate is guided by the guide plate.
