FUEL ADJUSTMENT DEVICE AND VEHICLE

There is disclosed a fuel adjustment device, including an ECU (10) and a catalyst (53) downstream oxygen sensor (SE4); ECU (10) controlling a fuel injection device (61) that causes an engine (5) to work; the catalyst downstream oxygen sensor (SE4) being provided downstream of a three-way catalyst (53) in an exhaust system attached to engine (5) and detects an oxygen concentration of an exhaust gas; ECU (10) adjusting a fuel supply amount such that an engine rotation speed decreases when the engine rotation speed reaches a first rotation speed (rs1); the first rotation speed (ra1) being the rotation speed corresponding to overspeeding; when the engine rotation speed decreases and reaches a second rotation speed (rs2), an amount of fuel being supplied to engine (5) is changed back to a normal amount; thereafter, when the engine rotation speed is continuously maintained in a monitoring range, the fuel supply amount being adjusted based on a detection result of the catalyst downstream oxygen sensor (SE4); the monitoring range is a range that includes the second rotation speed (rs2) and is lower than the first rotation speed (rs1).