The present invention provides a clock signal output circuit and a liquid crystal display device. The clock signal output circuit comprises a clock signal conversion unit, a voltage dividing unit, a protection signal generation unit, an over-current protection unit, and a switching unit. The protection signal generating unit comprises a subtractor, a comparator, a switch, a current source, and a capacitor. When the clock signal outputted from the clock signal output circuit is used to output the clock signal to the display panel, the peak current generated after the second ON of the quickly switching the machine on/off is flown through the voltage dividing unit so that the current source could not charge the voltage at the first terminal of the capacitor to a preset protection value, and when the peak current disappears, the current source can quickly charge the voltage at the first terminal of the capacitor to the preset protection value and input to the over-current protection unit to activate the overcurrent protection function, which is capable of preventing an over-current protection falsely triggered by a peak current generated when a liquid crystal display device is quickly switched on/off.