A hydrogen generator has a reaction chamber that contains a complex hydride capable of reacting with an aqueous acid solution to generate hydrogen. A storage chamber contains an aqueous acid solution that is supplied through a supply pipe to the reaction chamber to react with the complex hydride to generate hydrogen. The total weight of water contained in the aqueous acid solution is 0.2 times or more, but 3 times or less, than the weight of the complex hydride. A control device controls the supplying of the aqueous acid solution through the supply pipe to the reaction chamber based on a reference pressure such that the aqueous acid solution is repeatedly supplied to the reaction chamber when the reference pressure is greater than the internal pressure within the reaction chamber and not supplied to the reaction chamber when the reference pressure is less than the reaction chamber internal pressure.