LEAKAGE DIAGNOSING DEVICE OF IN-TANK CANISTER SYSTEM

PROBLEM TO BE SOLVED: To provide a leakage diagnosing device of an in-tank canister system capable of improving responsiveness during leakage diagnosis and accurately detecting a tank's internal pressure. SOLUTION: A three-way selector valve 47, and a leakage diagnosing passage 48 for directly communicating an intake system 33 of the internal combustion engine and the inside of a fuel tank 1 through the selector valve 47 during the leakage diagnosis are provided on the way of a purge passage 11. The selector valve 47 can switch between the purge passage during normal time and the leakage diagnosing passage during the leakage diagnosis. When negative pressure in the internal combustion engine is guided into the fuel tank 1, the negative pressure does not pass through a canister 2 and an evaporation passage 13. Therefore, pressure loss or the like of pipes on the ways of these passages does not affect to the detection by a pressure sensor 49. Thus, responsiveness during the leakage diagnosis is improved and the tank's internal pressure can be accurately detected.