An LED illuminator comprising: a rectifier; a first LED string connected to the rectifier and including a first partial LED string and a second partial LED string connected in series with the first partial LED string; a second LED string connected to the rectifier in parallel to the first LED string and including a third partial LED string and a fourth partial LED string connected in series with the third partial LED string; a first switching circuit configured to switch between a state where only the first partial LED string is connected to the 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 as the full-wave rectified voltage waveform that is output from the rectifier increases/decreases, wherein 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, characterised in that the first switching circuit is configured to detect a current that flows through at least part of the first LED string and to switch between a state where only the first partial LED string is connected to the rectifier and a state where the first partial LED string and the second partial LED string connected in series are connected to the rectifier in accordance with the detected current. a rectifier; a first LED string connected to the rectifier and including a first partial LED string and a second partial LED string connected in series with the first partial LED string; a second LED string connected to the rectifier in parallel to the first LED string and including a third partial LED string and a fourth partial LED string connected in series with the third partial LED string; a first switching circuit configured to switch between a state where only the first partial LED string is connected to the 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 as the full-wave rectified voltage waveform that is output from the rectifier increases/decreases, wherein 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, characterised in that the first switching circuit is configured to detect a current that flows through at least part of the first LED string and to switch between a state where only the first partial LED string is connected to the rectifier and a state where the first partial LED string and the second partial LED string connected in series are connected to the rectifier in accordance with the detected current.