An image forming apparatus includes a print head configured to fire ink droplets; a subtank configured to store therein ink and supply the ink to the print head; a subatmospheric pressure generating unit configured to generate subatmospheric pressure in the subtank; a main tank configured to supply ink to the subtank; a detecting unit configured to detect an amount of ink in the main tank; and a control unit configured to control the subatmospheric pressure generating unit to generate subatmospheric pressure in the subtank and control the print head to fire ink droplets when the detecting unit detects that an amount of ink in the main tank is less than a predetermined first threshold, and control the print head to stop firing ink droplets when a time elapsed after the subatmospheric pressure is generated in the subtank exceeds a predetermined second threshold.