A fuel injection system includes a vane-type fuel pump. The fuel pump has a first bypass passage with a first pressure relief valve for relieving pressurized fuel from a discharge passage downstream of a check valve to the discharge passage upstream of the check valve so that excess pressure in the discharge passage downstream of the check valve can be relieved to the discharge pressure upstream of the check valve. Therefore, fuel leakage through a fuel injection valve can be prevented for avoiding possibility of formation of overrich mixture even upon hot start condition.