When voltage changes occur in the battery used as a power supply in a fuel injection system, the amount of fuel injection also changes and the required amount of fuel injected cannot be obtained. To eliminate this problem, a fuel injector system is provided which has a fuel injection valve with at least one coil, a power supply, a power supply voltage detector, and a control unit for controlling the fuel injection valve. The control unit sets a reference value of a power supply voltages, and the above-mentioned fuel injection valve is controlled so as to obtain the required ampere-turns by reducing the resultant inductance of the coil when a power supply voltage detection value is less than the above-mentioned reference value, and the resultant inductance of the coil is increased when the power voltage detection value is greater than the reference value.