Method for stopping a hydrogen generator by controlling water supply to a reformer

A hydrogen generator includes: a reformer configured to generate a hydrogen-containing gas by a reforming reaction between a raw material and water; a heater configured to combust at least a part of the hydrogen-containing gas to supply heat necessary for the reforming reaction to the reformer; a combustion detector configured to detect a combustion state of the heater; a raw material supplier configured to supply the raw material; a water supplier configured to supply the water; and an operation controller. When stopping the hydrogen generator, the operation controller causes the raw material supplier to stop operating, the water supplier to stop operating in a case where the combustion detector detects extinction of flame, and the raw material supplier to start operating to supply the raw material to the hydrogen generator in a case where the reforming temperature detector detects a temperature equal to or lower than a reference temperature.