An image forming apparatus including a head part with an ejection port configured to eject ink, a discarded-ink tank configured to collect ejected or absorbed ink in order to restore a function of the ejection port, and a sensing device configured to sense the discarded ink collected in the discarded-ink tank, the sensing device including an absorber configured to absorb the ink and an optical sensor configured to sense the light received from the absorber is disclosed, wherein the apparatus uses ink having a characteristic such that the discarded ink is accumulated in a mountain-like shape in the discarded-ink tank, and the absorber is arranged at the location, at which discarded ink can be absorbed when a mountain top of the discarded ink accumulated in a mountain-like shape reaches a predetermined height so that the discarded ink flows along a slope of the discarded ink accumulated in a mountain-like shape to the absorber.