An overcurrent protection device of a power supply is provided. The overcurrent protection device includes an inductor, a first switch, a second switch, a feedback controller, a pulse width modulation (PWM) controller, and an overcurrent protection controller. The inductor may be connected to an input terminal of the power supply to which a current is inputted from a power source. The first switch may be connected between an output terminal of the inductor and a ground. The second switch may be connected between the output terminal of the inductor and an output terminal of the power supply. The feedback controller may compare an output voltage of the power supply with an output voltage target value, and generate a control voltage based on a result of comparing the output voltage and the output voltage target value. The PWM controller may control switch-on and switch-off of the first and second switches, and control a peak current of the first switch based on the control voltage. The overcurrent protection controller may include a timing capacitor charged with a current source proportional to the control voltage, and generate an overcurrent control signal for driving the PWM controller based on the control voltage. The overcurrent protection controller may charge the timing capacitor by the current source during a first switching period in which the second switch is turned on. When an output current exceeds a predetermined level regardless of an input voltage from the power source, an operation of the power supply may be stopped based on the overcurrent control signal.