The present disclosure provides a light emitting element drive device for driving a plurality of LED strings. The device comprises a power supply circuit, a plurality of current sources, a plurality of error amplifiers, a plurality of first diodes and a control circuit. The power supply circuit provides a driving voltage to each of the LED strings. The inverted input terminal of each error amplifier is coupled to a second terminal of the corresponding LED string. Each error amplifier output the voltage difference between the second terminal of the corresponding LED string and a first reference voltage. The anode of each first diode is coupled to the output terminal of the corresponding error amplifier, and the cathodes of the diodes are coupled to each other. The control circuit adjusts the driving voltage of the power supply circuit according to the cathode voltage of the conducted first diode.