To provide a vapor pressure measuring device capable of precisely computing vapor pressure without being affected by the external.

A fuel supplying system 10 includes: a fuel tank 20 storing fuel; a fuel pump 26 supplying the fuel in the fuel tank 20 to an injector 12; a nozzle 42; a vaporizing chamber 45; a venturi 47; a fuel vapor generating part 40 vaporizing the fuel in the vaporizing chamber 45 by jetting the fuel from the nozzle 42 to pass through the venturi 47; a first fuel passage 22 connecting the fuel pump 26 with the injector 12; a second fuel passage 23 whose one end is connected with the fuel pump and other end is connected with the fuel vapor generating part 40; a pressure sensor 46 detecting the pressure in the fuel vapor generating part 40; and an ECU 30 computing the vapor pressure of the fuel based on the detection results of the pressure sensor 46. The fuel vapor generating part 40 is arranged in the fuel tank 20.