A method of operating a hydrogen generation apparatus, the hydrogen generation apparatus including: a first desulfurizer being packed with an adsorption desulfurization agent, the adsorption desulfurization agent configured to remove a sulfur component from a raw material gas at both operating temperatures and non-operating temperatures of the hydrogen generation apparatus; a second desulfurizer configured to remove the sulfur component from the raw material gas by hydrogenating the sulfur component; a reformer configured to generate a hydrogen-containing reformed gas from the raw material gas from which the sulfur component has been removed by at least one of the first desulfurizer and the second desulfurizer; and a recycle passage through which a part of the reformed gas generated by the reformer is mixed into the raw material gas that is to be supplied to the second desulfurizer, characterized in that the second desulfurizer includes a catalyst in an unreduced state, the catalyst requiring a reduction treatment in order to be activated, the method comprising: after installation or maintenance of the hydrogen generation apparatus, supplying the raw material gas to the reformer through the first desulfurizer until the unreduced catalyst in the second desulfurizer is activated by a mixed gas of the reformed gas supplied through the recycle passage and the raw material gas; and after the catalyst in the second desulfurizer is activated, supplying the raw material gas to the reformer through the second desulfurizer by bypassing the first desulfurizer. a first desulfurizer being packed with an adsorption desulfurization agent, the adsorption desulfurization agent configured to remove a sulfur component from a raw material gas at both operating temperatures and non-operating temperatures of the hydrogen generation apparatus; a second desulfurizer configured to remove the sulfur component from the raw material gas by hydrogenating the sulfur component; a reformer configured to generate a hydrogen-containing reformed gas from the raw material gas from which the sulfur component has been removed by at least one of the first desulfurizer and the second desulfurizer; and a recycle passage through which a part of the reformed gas generated by the reformer is mixed into the raw material gas that is to be supplied to the second desulfurizer, characterized in that the second desulfurizer includes a catalyst in an unreduced state, the catalyst requiring a reduction treatment in order to be activated, the method comprising: after installation or maintenance of the hydrogen generation apparatus, supplying the raw material gas to the reformer through the first desulfurizer until the unreduced catalyst in the second desulfurizer is activated by a mixed gas of the reformed gas supplied through the recycle passage and the raw material gas; and after the catalyst in the second desulfurizer is activated, supplying the raw material gas to the reformer through the second desulfurizer by bypassing the first desulfurizer. after installation or maintenance of the hydrogen generation apparatus, supplying the raw material gas to the reformer through the first desulfurizer until the unreduced catalyst in the second desulfurizer is activated by a mixed gas of the reformed gas supplied through the recycle passage and the raw material gas; and after the catalyst in the second desulfurizer is activated, supplying the raw material gas to the reformer through the second desulfurizer by bypassing the first desulfurizer.