A fuel cell system, comprising: a hydrogen generation apparatus (50, 60, 70); and a fuel cell, the hydrogen generation apparatus (50, 60, 70) comprising: a reforming unit that reforms a raw material to generate a hydrogen-containing gas for supply to the fuel cell as a fuel gas; a raw material supply device that supplies the raw material to the reforming unit; a water supply device that supplies water to the reforming unit; and a combustor that combusts the raw material or part of the fuel gas which is not consumed at the fuel cell; a combustion air supply device that supplies combustion air to the combustor; and a hydrogen generation amount detection unit (3a, 13, 14, 8) that detects an amount of the hydrogen-containing gas generated; and a controller; and wherein the fuel cell performs power generation by using the hydrogen-containing gas that is supplied from the hydrogen generation apparatus (50, 60, 70), characterized in that when a parameter that contributes to the amount of the hydrogen-containing gas generated is in a predetermined range, or when an amount of variation in a parameter that contributes to the amount of the hydrogen-containing gas generated is in a predetermined range, the controller is configured to drive the raw material supply device by setting a control parameter corresponding to a relatively low heat amount gas in a case where the amount of the hydrogen-containing gas generated decreases, and is configured to drive the raw material supply device by setting a control parameter corresponding to a relatively high heat amount gas in a case where the amount of the hydrogen-containing gas generated increases, wherein the control parameter is any one of an amount of the supplied raw material, an amount of water supplied, and a flow rate of the combustion air, and wherein the parameter is at least one of a composition of the raw material, an ambient environment temperature, and a pressure of the raw material. a hydrogen generation apparatus (50, 60, 70); and a fuel cell, the hydrogen generation apparatus (50, 60, 70) comprising: a reforming unit that reforms a raw material to generate a hydrogen-containing gas for supply to the fuel cell as a fuel gas; a raw material supply device that supplies the raw material to the reforming unit; a water supply device that supplies water to the reforming unit; and a combustor that combusts the raw material or part of the fuel gas which is not consumed at the fuel cell; a combustion air supply device that supplies combustion air to the combustor; and a hydrogen generation amount detection unit (3a, 13, 14, 8) that detects an amount of the hydrogen-containing gas generated; and a controller; and a reforming unit that reforms a raw material to generate a hydrogen-containing gas for supply to the fuel cell as a fuel gas; a raw material supply device that supplies the raw material to the reforming unit; a water supply device that supplies water to the reforming unit; and a combustor that combusts the raw material or part of the fuel gas which is not consumed at the fuel cell; a combustion air supply device that supplies combustion air to the combustor; and a hydrogen generation amount detection unit (3a, 13, 14, 8) that detects an amount of the hydrogen-containing gas generated; and a controller; and wherein the fuel cell performs power generation by using the hydrogen-containing gas that is supplied from the hydrogen generation apparatus (50, 60, 70), characterized in that when a parameter that contributes to the amount of the hydrogen-containing gas generated is in a predetermined range, or when an amount of variation in a parameter that contributes to the amount of the hydrogen-containing gas generated is in a predetermined range, the controller is configured to drive the raw material supply device by setting a control parameter corresponding to a relatively low heat amount gas in a case where the amount of the hydrogen-containing gas generated decreases, and is configured to drive the raw material supply device by setting a control parameter corresponding to a relatively high heat amount gas in a case where the amount of the hydrogen-containing gas generated increases, wherein the control parameter is any one of an amount of the supplied raw material, an amount of water supplied, and a flow rate of the combustion air, and wherein the parameter is at least one of a composition of the raw material, an ambient environment temperature, and a pressure of the raw material.