To provide a carriage driving system by which position and speed of a carriage can be highly accurately controlled even when amount of the ink in an ink cartridge is changed and its weight is changed and an ink-jet printer.

In the carriage driving system for the ink-jet printer comprising a carriage driving mechanism 1 and a controller for controlling the mechanism and wherein the carriage driving mechanism 1 has a motor 11, a carriage moving mechanism (a pulley 12 with a groove and a belt 13 with teeth) driven by the motor and a carriage 14 moving back and forth in the main scanning direction by means of the carriage moving mechanism and on which the ink cartridge 15 is mounted, the controller changes the control constant in accordance with decrease in the amount (q) of the ink in the ink cartridge 15.