An ink tank of the foam type which is provided with a detected portion capable of exactly and surely detecting the amount of ink used by the printer or remaining in the ink tank. The ink tank includes a sub ink chamber that is disposed or formed between a main ink chamber and an ink outlet of an ink tank of a foam type. When an amount of air flowing into the sub ink chamber increases, one or more reflecting surfaces of a right-angled prism, which function as ink interfaces, resume their original function of reflecting surfaces, thereby enabling the detection of an ink end. Air bubbles having entered the sub ink chamber are surely led onto the one or more reflecting surfaces by a bubble storage part. At an ink passage having a narrow width, which is defined by the one or more reflecting surfaces, air bubbles are pressed against the one or more reflecting surfaces to be put to a crushed state and in surface contact with the latter. Air bubbles are surely led onto the one or more reflecting surfaces, and are crushed and pressed against the reflecting surfaces. This configuration prevents the one or more reflecting surfaces from being covered with ink retained in spaces among the air bubbles. Therefore, the ink end can be detected surely and exactly.