A protection circuit includes a first power supply system including a first power supply and a first ground, a second power supply system including a second power supply and a second ground, and a control circuit that, when coupled to an electro-static discharge (ESD) stress being applied to the first power supply system, controls a first switch. The first switch is provided between the signal line and the first ground. The control circuit includes a capacitance element, a resistance element in series with the capacitance element, and an inverter, an output of the inverter being connected between a gate of the first switch, an input of the inverter being connected to a connecting point between the capacitance element and the resistance element.