A vaporized fuel treatment device includes a sealing valve disposed in a vapor passage between a fuel tank and a canister and is configured to include a valve element moves forward and backward in an axial direction to a valve seat, a cut-off valve configured to cut off a communication between the canister and an atmosphere, a tank internal pressure sensor detects an internal pressure of the fuel tank, and a canister internal pressure sensor that detects an internal pressure of the canister, a controller programmed to change an axial distance between the valve element and the valve seat in a state where the cut-off valve cuts off the communication between the canister and the atmosphere and to learn a valve opening start position of the sealing valve based on changes in the internal pressures of the fuel tank and the canister depending on a change in the axial distance.