Disclosed is an automatic tablet feeding apparatus. The automatic tablet feeding apparatus includes a guide duct having a receiving space defined therein to receive tablets introduced thereinto and guide the tablets downward, a slider formed to be inclined downward toward the receiving space, a first vibrator accommodated in an outer side portion of the slider and configured to output vibration energy in response to an external control signal, a vibrator controller configured to control the frequency of the first vibrator, and an elastic support plate received in an outer side surface of the slider. The vibrator controller includes a smoothing circuit unit smoothing a DC voltage, a main controller generating a PWM control signal, and a voltage variable switching unit varying the DC voltage smoothed by the smoothing circuit unit in response to the PWM control signal from the main controller and applying the DC voltage to the first vibrator.