To provide a liquid cooling system for an electric component mounted in an aircraft, in which a flow rate of a coolant fed to the electric component mounted in the aircraft is optimized by a simple method, a liquid cooling system 1 for an electric component mounted in an aircraft adopts a flow rate adjusting valve which is a thermostat valve 5 such that the opening degree of the valve increases with an increase in the temperature of the coolant flowing into the flow rate adjusting valve so as to raise the flow rate of the coolant fed to the electric component 50, and the opening degree of the valve decreases with a decrease in the temperature of the coolant flowing into the flow rate adjusting valve so as to reduce the flow rate of the coolant fed to the electric component 50.