At least two or more than two ink-jet recording heads provided with respective discharge ports for discharging ink are arranged in the direction of conveyance of recording medium. The inks filled in the respective ink-jet recording heads are made to show different surface tensions. With this arrangement, as inks are discharged onto the recording medium that is conveyed by a conveyor under the control of a drive section, the image formed by the inks discharged onto the recording medium shows an improved quality.