A hydrogen fuel assist device for an internal combustion engine includes: a hydrogen gas generator for generating hydrogen gas; a fluid pump capable of pumping the hydrogen gas into a combustion chamber of the internal combustion engine through an air throttle valve, which is connected to the combustion chamber, at varying flow rates; and a pump controller for controlling a rotational speed of the fluid pump in response to opening degree of a fuel throttle valve connected to the combustion chamber so as to adjust the flow rate of the hydrogen gas to be supplied into the combustion chamber during operation of the internal combustion engine.