Provided is a liquid ejection apparatus including an ink cartridge including a first ink storage section which stores ink; an ink tank including a second ink storage section which is connected to the ink cartridge and supplied with ink from the ink cartridge; and a detection unit including a light emitting section which emits detection light and a light receiving section which receives the detection light, in which the ink cartridge includes a first protrusion in communication with the first ink storage section, the ink tank includes a recess and a second protrusion in communication with the second ink storage section, the light emitting section and the light receiving section are arranged in the recess, and the first protrusion and the second protrusion are arranged between the light emitting section and the light receiving section.