An organic light emitting display device comprising: a display panel including subpixels, wherein each subpixel includes an organic light emitting diode; a power supply unit including a power generation transistor, the power supply unit being configured to control the power generation transistor according to a switching clock signal to generate and supply a first source voltage (VDDEL) to the organic light emitting diodes of the subpixels of the display panel; a driving device configured to drive the display panel and including at least one of a scan driver, a data driver and a timing controller, and a power control unit configured to perform control such that one or more of synchronization signals of the at least one of the scan driver, the data driver, and the timing controller and a switching frequency of the switching clock signal of the power generation transistor of the power supply unit are synchronized characterized in that the power control unit is adapted to vary a driving period of the one or more synchronization signals of the driving device of the display panel in synchronization with the switching frequency of the switching clock signal of the power generation transistor of the power supply unit, wherein the power control unit comprises a frequency divider configured to receive the switching clock signal from the power supply unit, to generate a DATA output clock signal of a low frequency corresponding to an integer multiple of the switching frequency of the switching clock signal, and to output the DATA output clock signal to the driving device in order to vary the driving period of the one or more synchronization signals in synchronization with the switching frequency of the switching clock signal. a display panel including subpixels, wherein each subpixel includes an organic light emitting diode; a power supply unit including a power generation transistor, the power supply unit being configured to control the power generation transistor according to a switching clock signal to generate and supply a first source voltage (VDDEL) to the organic light emitting diodes of the subpixels of the display panel; a driving device configured to drive the display panel and including at least one of a scan driver, a data driver and a timing controller, and a power control unit configured to perform control such that one or more of synchronization signals of the at least one of the scan driver, the data driver, and the timing controller and a switching frequency of the switching clock signal of the power generation transistor of the power supply unit are synchronized characterized in that the power control unit is adapted to vary a driving period of the one or more synchronization signals of the driving device of the display panel in synchronization with the switching frequency of the switching clock signal of the power generation transistor of the power supply unit, wherein the power control unit comprises a frequency divider configured to receive the switching clock signal from the power supply unit, to generate a DATA output clock signal of a low frequency corresponding to an integer multiple of the switching frequency of the switching clock signal, and to output the DATA output clock signal to the driving device in order to vary the driving period of the one or more synchronization signals in synchronization with the switching frequency of the switching clock signal.