An LED illuminator configured to further reduce total harmonic distortion is provided. The LED illuminator has: a first LED string including a first partial LED string and a second partial LED string; a second LED string including a third partial LED string and a fourth partial LED string; a first switching circuit configured to switch between a state where only the first partial LED string is connected to a rectifier and a state where the first partial LED string and the second partial LED string connected in series are connected to the rectifier as a full-wave rectified voltage waveform that is output from the rectifier increases/decreases; and a second switching circuit configured to switch between a state where only the third partial LED string is connected to the rectifier and a state where the third partial LED string and the fourth partial LED string connected in series are connected to the rectifier, and the switching timing by the first switching circuit and the switching timing by the second switching circuit are set so as to differ from each other.
