PURPOSE: To stably and efficiently produce a gasoline which has an octane number near enough to an objective octane number even when the gasoline fluctuates in composition.

CONSTITUTION: A process for continuously producing a gasoline having an octane number as an objective value, wherein the measured octane number X1 and the computed octane number Y1 of the produced gasoline or a gasoline having a similar composition at time 1 during the practice of the process or a preparatory process thereof are specified; the computed octane number Y2 of the produced gasoline at arbitrary suitable time 2 during this process is determined; the actual octane number of the produced gasoline at time 2 is estimated on the basis of at least the measured number X1, the computed number Y1 and the computed number Y2; and the rate of the high-octane-number component in the gasoline is increased when the estimated number B is smaller than the objective octane number A, or the rate of the low-octane-number component in the gasoline is increased when the estimated octane number B is larger than the objective octane number A so that the octane number of the produced gasoline may be equal or near to the objective octane number, is provided.