A fuel cell system, comprising: a fuel cell including an anode to which an anode gas is supplied and a cathode to which a cathode gas is supplied; a reformer for forming the anode gas by reforming a source gas; a source gas passage for supplying the source gas to the reformer; a gas conveying source provided at the source gas passage and supplying the source gas to the reformer via the source gas passage; a desulfurizer ( 100, 200) provided at the source gas passage for desulfurizing the source gas; and a sensor detecting a physical quantity related to a dew point or a humidity of the source gas supplied to the desulfurizer ( 100, 200), characterized by a control portion, which is configured to obtain a remaining lifetime of the desulfurizer ( 100, 200) on the basis of an information value indicating a ratio of a first physical quantity ( A, A1, A2) detected by the sensor to a second physical quantity ( B, B1, B2) detected by the sensor or a ratio of the second physical quantity ( B, B1, B2) to the first physical quantity ( A, A1, A2), and to output maintenance information for conducting a maintenance of the desulfurizer ( 100, 200) when an end of the obtained remaining lifetime of the desulfurizer ( 100, 200) is earlier than a preset timing of next routine maintenance, wherein the first physical quantity ( A, A1, A2) relates to a cumulative operation time of the fuel cell system from a reference timing, and the second physical quantity ( B, B1, B2) relates to a cumulative operation time from the reference timing during which the source gas having a dew point equal to or higher than a predetermined level or having a humidity equal to or higher than a predetermined level is supplied via the source gas passage, and wherein the first physical quantity ( A, A1, A2) and the second physical quantity ( B, B1, B2) have physical quantities of the same unit. a fuel cell including an anode to which an anode gas is supplied and a cathode to which a cathode gas is supplied; a reformer for forming the anode gas by reforming a source gas; a source gas passage for supplying the source gas to the reformer; a gas conveying source provided at the source gas passage and supplying the source gas to the reformer via the source gas passage; a desulfurizer ( 100, 200) provided at the source gas passage for desulfurizing the source gas; and a sensor detecting a physical quantity related to a dew point or a humidity of the source gas supplied to the desulfurizer ( 100, 200), characterized by a control portion, which is configured to obtain a remaining lifetime of the desulfurizer ( 100, 200) on the basis of an information value indicating a ratio of a first physical quantity ( A, A1, A2) detected by the sensor to a second physical quantity ( B, B1, B2) detected by the sensor or a ratio of the second physical quantity ( B, B1, B2) to the first physical quantity ( A, A1, A2), and to output maintenance information for conducting a maintenance of the desulfurizer ( 100, 200) when an end of the obtained remaining lifetime of the desulfurizer ( 100, 200) is earlier than a preset timing of next routine maintenance, wherein the first physical quantity ( A, A1, A2) relates to a cumulative operation time of the fuel cell system from a reference timing, and the second physical quantity ( B, B1, B2) relates to a cumulative operation time from the reference timing during which the source gas having a dew point equal to or higher than a predetermined level or having a humidity equal to or higher than a predetermined level is supplied via the source gas passage, and wherein the first physical quantity ( A, A1, A2) and the second physical quantity ( B, B1, B2) have physical quantities of the same unit.