Disclosed is a light emitting diode (LED) illuminating apparatus having enhanced stability of the quantity of light. The LED illuminating apparatus includes an LED lighting block connected to a rectified voltage and including at least one LED module, an alternative reference voltage generating block configured to detect the rectified voltage and generate an alternative reference voltage, and a switching block connected to the tap and configured to form a closed circuit including the at least one LED module. The at least one LED module includes a cathode terminal having a tap. The alternative reference voltage has a voltage level according to a root mean square (RMS) value of the rectified voltage. The amount of currents flowing through the closed circuit is controlled by the alternative reference voltage to have a negative relationship with the RMS value of the rectified voltage. In an LED illuminating apparatus according to the present invention, degradation in uniformity of light due to instability of an input power is reduced.