The hydrogen generator includes: a reformer 101 having a reforming catalyst configured to cause a source material and water to react with each other to generate a hydrogen-rich reformed gas; a reformer heater 104 configured to heat the reformer; a carbon monoxide reducing portion 111,121 having a carbon monoxide reducing catalyst configured to reduce carbon monoxide contained in the reformed gas; a carbon monoxide reduction heater 112,123 configured to heat at least one of the carbon monoxide reducing portion, the carbon monoxide reducing catalyst and the reformed gas passing through the carbon monoxide reducing portion; and a controller 200 capable of control such that the carbon monoxide reduction heater is caused to operate in a stop operation period.