A method is provided for setting a target moving velocity of a carriage in an image forming apparatus wherein a recording head is driven at a driving frequency proportional to a moving velocity of the carriage. The method includes steps of: varying the driving frequency of the recording head proportional to the moving velocity of the carriage so as to measure an ejection velocity of ink droplets ejected from nozzles of the recording head; deriving a velocity range where the ejection velocity of ink droplets from the nozzles of the recording head is increased as the moving velocity of the carriage is increased; calculating a control error between the target moving velocity and an actual moving velocity of the carriage; and setting the target moving velocity of the carriage such that the actual moving velocity of the carriage is within the velocity range based on the calculated control error.