PURPOSE: To enable distillation property to be correctly detected, in the controller in the caption for compensating an increased fuel quantity at the time of high distillation property of fuel, by opening, before detection, a steam introducing passage and a steam exhausting passage for setting the atmospheric pressure, in a steam chamber inside a fuel tank, while closing them at the time of the detection.

CONSTITUTION: A steam reserving container 7 with its opening 7a facing downwardly under an oil surface is set in a fuel tank 6, while a steam chamber 8 is formed above the oil surface in the container 7. To the steam chamber 8 are connected a new air introducing passage 9 intercommunicating to the upstream side of a throttle valve 5 on the way of an intake-air passage 2 and a steam exhausting passage 10 intercommunicating to the downstream side thereof, wherein an outside air intake valve 11 and a steam exhaust valve 13 are disposed, respectively. At the time of ignitionon, on the basis of a temperature sensor 14 and a pressure sensor 15 installed inside the steam chamber 8, a controller 12 determines temperature and pressure inside the steam chamber 8 with the valves 11, 13 closed so as to open the valves 11, 13. And further, on the basis of a difference between the pressure inside the steam chamber 8 and the value of an outer atmospheric pressure sensor 21, a saturated steam pressure is calculated so that distillation property is judged.