A fuel tank system for a vehicle having an internal combustion engine, the fuel tank system comprising: a fuel storage unit having a sealing valve and configured to seal a fuel tank that stores fuel; a processing unit configured to process fuel evaporative gas in the fuel tank; and a control unit configured to diagnose a failure of the fuel storage unit and the processing unit, wherein the fuel storage unit includes a first pressure detection unit configured to detect a pressure of the fuel tank, and a second pressure detection unit disposed at a position different from the first pressure detection unit and configured to detect a pressure of the fuel tank, tanle, and a vapor passage through which the fuel tank and the sealing valve are communicated with each other, wherein the processing unit includes a purge passage through which the sealing valve and an intake passage of the internal combustion engine are communicated with each other, a first on-off valve configured to be opened and closed between the intake passage and the purge passage, a canister connected to the purge passage between the sealing valve and the first on-off valve and configured to adsorb fuel evaporative gas in the fuel tank, and a pressure generation unit connected to the canister and configured to generate pressure, and wherein the control unit is configured to specify a presence or an absence of a clogging of the vapor passage based on a first pressure value detected by the first pressure detection unit and a second pressure value detected by the second pressure detection unit when the pressure in the fuel tank is changed by the pressure generation unit in a condition that the sealing valve is controlled to be opened. a fuel storage unit having a sealing valve and configured to seal a fuel tank that stores fuel; a processing unit configured to process fuel evaporative gas in the fuel tank; and a control unit configured to diagnose a failure of the fuel storage unit and the processing unit, wherein the fuel storage unit includes a first pressure detection unit configured to detect a pressure of the fuel tank, and a second pressure detection unit disposed at a position different from the first pressure detection unit and configured to detect a pressure of the fuel tank, tanle, and a vapor passage through which the fuel tank and the sealing valve are communicated with each other, a first pressure detection unit configured to detect a pressure of the fuel tank, and a second pressure detection unit disposed at a position different from the first pressure detection unit and configured to detect a pressure of the fuel tank, tanle, and a vapor passage through which the fuel tank and the sealing valve are communicated with each other, wherein the processing unit includes a purge passage through which the sealing valve and an intake passage of the internal combustion engine are communicated with each other, a first on-off valve configured to be opened and closed between the intake passage and the purge passage, a canister connected to the purge passage between the sealing valve and the first on-off valve and configured to adsorb fuel evaporative gas in the fuel tank, and a pressure generation unit connected to the canister and configured to generate pressure, and a purge passage through which the sealing valve and an intake passage of the internal combustion engine are communicated with each other, a first on-off valve configured to be opened and closed between the intake passage and the purge passage, a canister connected to the purge passage between the sealing valve and the first on-off valve and configured to adsorb fuel evaporative gas in the fuel tank, and a pressure generation unit connected to the canister and configured to generate pressure, and wherein the control unit is configured to specify a presence or an absence of a clogging of the vapor passage based on a first pressure value detected by the first pressure detection unit and a second pressure value detected by the second pressure detection unit when the pressure in the fuel tank is changed by the pressure generation unit in a condition that the sealing valve is controlled to be opened.