Evaporated fuel processing device

An evaporated fuel processing device comprising:

• a canister disposed between a fuel tank and an intake passage, and configured to store evaporated fuel generated in the fuel tank;
• a pump configured to pump purge gas toward the intake passage through a purge passage connecting the canister and the intake passage, the purge gas including the evaporated fuel stored in the canister;
• a detecting unit configured to detect a specific pressure difference between a pressure of gas that has passed through the canister and the pump and a pressure of the gas before passing through the canister and the pump;
• and
• an estimating unit configured to estimate a flow rate of the purge gas supplied to the intake passage using the specific pressure difference,
• wherein
• a flow rate of the gas pumped out from the pump is higher with a smaller pressure difference between upstream and downstream sides relative to the pump,
• the flow rate of the gas pumped out from the pump is higher with a higher density of the purge gas,
• a flow rate of the gas supplied from the canister is lower with a smaller pressure difference between upstream and downstream sides relative to the canister,
• the flow rate of the gas supplied from the canister is lower with a higher density of the purge gas, and
• the estimating unit estimates the flow rate of the purge gas while the specific pressure difference is an unchanged pressure difference, the unchanged pressure difference being a pressure at which the flow rate of the gas is not changed due to the density of the purge gas.