To provide a mixed fuel generating device capable of generating hardly-separable mixed fuel mixed by sufficiently atomizing water and air.

This mixed fuel generating device has a suction side mixer 12 connected to the suction side of a pump 60 and supplying the mixed fuel of mixing the water and the air flowing in by suction of the pump 60 to the suction side of the pump 60, and a discharge side mixer 14 connected to the discharge side of the pump 60 and discharging the mixed fuel from the pump 60 by further mixing. The mixed fuel from the discharge side mixer 14 is supplied to an internal combustion engine 1. The device has a mixing tank 8 for storing the mixed fuel discharged from the discharge side mixer 14, and also has a fuel tank 4 for storing fuel and a water tank 6 for storing the water, and is provided with a switching valve 16 for switching the inflow to the suction side mixer 12 from the fuel tank 4 and the water tank 6 or from the inside of the mixing tank 8.