A fuel vapor processing device includes a three-way valve having a common valve chamber in which a first valve body, a second valve body, and a third valve body are housed. A single pressure sensor is provided in the common valve chamber. The first valve body enables communication between the common valve chamber and a first valve chamber. The second valve body enables communication between the common valve chamber and a second valve chamber communicating with an inside of the canister. The third valve body enables communication between the common valve chamber and a third valve chamber communicating with an inside of a fuel tank. An ECU controls the three-way valve and a switching valve, and controls driving of a pump to perform fuel vapor leak diagnosis for the fuel tank and the canister, based on a detection value detected by the pressure sensor.