The present invention reduces a difference in speed between a main drop section and a tailing section of a ejected ink droplet by heating a front heater (29f) and a rear heater (29b) provided for one nozzle with a predetermined time lag and thus, the ink dot formed from the main drop section and the tailing section on a printing medium can be more approximate to a circle. Thereby, it is possible to prevent print quality from being degraded by the tailing section separated from the main drop section of the ink droplet ejected from an ink jet printing apparatus of serial type.