A fuel cell system comprising: a fuel cell configured to generate power by using a fuel gas and an oxidant gas; a fuel gas supply path configured to supply the fuel gas to an anode entrance of the fuel cell; a recycling path configured to return anode off-gas which is discharged from an anode exit of the fuel cell to the anode entrance of the fuel cell; an anode off-gas discharge path that branches from the recycling path and configured to discharge the anode off-gas to an outside; a first valve that is provided in the anode off-gas discharge path; a pressurizer that is provided in the recycling path and configured to pressurize the anode off-gas which flows through the recycling path and the anode off-gas is thereby caused to flow into the fuel gas supply path; and a controller; characterized in that the controller is configured to (i) control the pressurizer to act in at least one of a timing in execution of a purge action in which the fuel gas is supplied from the fuel gas supply path and the anode off-gas is discharged to the outside in a state where the first valve is opened and a timing in prescribed time after the purge action, and (ii) assess abnormality, while the control is executed, based on a pressure of the anode off-gas that flows through the recycling path or the anode off-gas discharge path, or an action amount of the pressurizer, wherein the action amount of the pressurizer is an output of the pressurizer, wherein the controller is configured to assess that abnormality is present when the pressure of the anode off-gas that flows through the recycling path that is upstream of the pressurizer or the pressure of the anode off-gas that flows through the anode off-gas discharge path is a first threshold value or more. a fuel cell configured to generate power by using a fuel gas and an oxidant gas; a fuel gas supply path configured to supply the fuel gas to an anode entrance of the fuel cell; a recycling path configured to return anode off-gas which is discharged from an anode exit of the fuel cell to the anode entrance of the fuel cell; an anode off-gas discharge path that branches from the recycling path and configured to discharge the anode off-gas to an outside; a first valve that is provided in the anode off-gas discharge path; a pressurizer that is provided in the recycling path and configured to pressurize the anode off-gas which flows through the recycling path and the anode off-gas is thereby caused to flow into the fuel gas supply path; and a controller; characterized in that the controller is configured to (i) control the pressurizer to act in at least one of a timing in execution of a purge action in which the fuel gas is supplied from the fuel gas supply path and the anode off-gas is discharged to the outside in a state where the first valve is opened and a timing in prescribed time after the purge action, and (ii) assess abnormality, while the control is executed, based on a pressure of the anode off-gas that flows through the recycling path or the anode off-gas discharge path, or an action amount of the pressurizer, wherein the action amount of the pressurizer is an output of the pressurizer, (i) control the pressurizer to act in at least one of a timing in execution of a purge action in which the fuel gas is supplied from the fuel gas supply path and the anode off-gas is discharged to the outside in a state where the first valve is opened and a timing in prescribed time after the purge action, and (ii) assess abnormality, while the control is executed, based on a pressure of the anode off-gas that flows through the recycling path or the anode off-gas discharge path, or an action amount of the pressurizer, wherein the action amount of the pressurizer is an output of the pressurizer, wherein the controller is configured to assess that abnormality is present when the pressure of the anode off-gas that flows through the recycling path that is upstream of the pressurizer or the pressure of the anode off-gas that flows through the anode off-gas discharge path is a first threshold value or more.