NOVELTY - The device comprises a current-voltage control unit converting the battery power into a predetermined current and voltage output. An ion receiving liquid reservoir accommodates a hydroxide ion aqueous solution. A water supply valve generates a switching control signal according to the hydroxide ion aqueous solution shortage occurrence. A first coil is wound around a reaction core, and discharges the reaction heat generated in the core to outside, where the coil is made of stainless material. A hydrogen generation part generates hydrogen through the electrolysis.    USE - The environment-friendly fuel saving device is useful for generating hydrogen that is used as an auxiliary fuel in an internal combustion engine of a vehicle i.e. car, and in a ship engine.    ADVANTAGE - The body negative plate is made of the stainless material, and the heat generated in the in the coil can be released to the outside so that the lifetime of the device is increased. The device can be easily mounted at a secondary hydrogen vehicle or a vessel in a compact manner, reduces the usage of the main fuel e.g. gasoline or whale-oil so that the combustion efficiency of the vehicle is increased. The device has reduced weight, and automatically controls the supply of the auxiliary fuel, thus increasing the energy efficiency of the vehicle.    DETAILED DESCRIPTION - The device comprises a current-voltage control unit for converting the battery power received from a vehicle or vessel into a predetermined current and voltage output. An ion receiving liquid reservoir accommodates a hydroxide ion aqueous solution. A water supply valve generates a switching control signal according to the hydroxide ion aqueous solution shortage occurrence. A first coil is wound around a reaction core, applies the anode voltage to a transformer from the control unit, and discharges the reaction heat generated in the core to outside, where the coil is made of stainless material. The transformer is equipped with a body negative plate to receive a body. The first coil is dipped in the hydroxide ion aqueous solution. A part generates hydrogen through the electrolysis. A controller indicates the switching control signal through a lamp. The first coil is wound around an outer periphery of the reaction core. The body negative plate emits the heat generated in the reaction core to the outside, where the current-voltage control unit is changed with 4-12 V direct current.