A current source device controls a rate of change of current flowing through a load so that the change rate of the current is equal to a change rate of a fluctuating supply voltage. A first transistor is fed with the supply voltage via a first resistor connected to its collector and a second resistor connected to its emitter. A second transistor has a base connected to a base of the first transistor, an emitter connected to a third resistor and a collector connected to a load. A current to the load is fed from the supply voltage via the load, the collector and emitter of the second transistor and the third resistor. The collector and base of the first transistor are respectively connected to a base and an emitter of a third transistor having a collector fed with the supply voltage. The ratio between a voltage drop caused across the second resistor by a reference current flowing through the first resistor, the collector and emitter of the first transistor and the second resistor, and a voltage drop caused across the third resistor by an emitter current of the second transistor, which is substantially equal to a collector current of the second transistor flowing through the load, is set to a predetermined value. The emitter area of the second transistor is enlarged beyond that of the first transistor to obtain a sufficiently large output current.