In a combustor, divisional fluid passages of a first group, and divisional fluid passages of a second group are present on an inner peripheral side, and divisional fluid passages are also present on an outer peripheral side, and swirl air flows are gushed from the divisional fluid passages. When the total amount of fuel supplied to the combustor is small as in a speed increasing state or in a low load state, fuel is injected only into the divisional fluid passages of the first group. Since a fuel injection region is limited to a position on the inner peripheral side, particularly, a specific position, the concentration of a fuel gas comprising a mixture of fuel and air is lean, but is higher than a flammability limit concentration, even when the total amount of fuel is small.