To start operation of an internal combustion engine at low temperature securely by a simple configuration to improve fuel economy.

In this fuel controller for the internal combustion engine provided with an on-vehicle fuel separator 30 for separating gasoline from alcohol mixed gasoline and operating the on-vehicle fuel separator 30 if amount of gasoline stored in a subtank 33 for gasoline does not reach the amount demanded at operation start time of the engine 10 at low temperature to increase the amount of stored gasoline, concentration of gasoline in the alcohol mixed gasoline is obtained before operating the on-vehicle fuel separator 30, and insufficient amount of gasoline is displayed in a display part 42 without operating the on-vehicle fuel separator 30, that is, without driving a feed pump 21, etc. if the concentration is zero (concentration of alcohol is 100%) to urge a user to feed gasoline into a vehicle.