Device and method for diagnosing evaporated fuel processing device

A diagnostic apparatus for an evaporated fuel processing apparatus, wherein the evaporated fuel processing apparatus includes a blocking valve configured to selectively allow and shut off communication between a canister and a fuel tank, and maintains the fuel tank in hermetic state by closing the blocking valve while a vehicle is stationary, and adsorbs evaporated fuel by the canister by opening the blocking valve during fuel filling, wherein the evaporated fuel occurs in the fuel tank, the diagnostic apparatus comprising:

• a pump connected to a canister-side region with respect to the blocking valve, and configured to pressurize an inside of a system, wherein the system includes the canister and the fuel tank;
• and
• at least one pressure sensor configured to sense an internal pressure of the system;
• wherein the diagnostic apparatus is configured to:
• start pressurization by the pump with the blocking valve closed;
• bring the inside of the system into a pressurized state by opening the blocking valve with a delay of a predetermined period after the start of pressurization;
• and
• perform a leakage diagnosis based on a change in the internal pressure of the system from the pressurized state.