Results of recent satellite observations indicate that a large amount of O+ are escaping from the terrestrial ionosphere into the magnetosphere. However, either the global distribution or the temporal variation of such O+ escape has not been understood well yet. A 2-Dimensional observation of oxygen ion emission (e.g., O II 83.4 nm) provides crucial information on the oxygen escape processes. In order to establish the basic technology required for such a 2-D (i.e., imaging) observation, we have developed an eXtreme Ultra-Violet (XUV) sensor sensitive to the O II 83.4-nm emission. In this study we present recent results of the observation of O+ ion escape from the ionosphere in the polar cap region using our XUV sensor carried by the sounding rocket SS-520-2. The XUV sensor successfully obtained an altitudinal profile of the intensity of the O II emission from 150 km through 1100 km of altitudes and detected 5--6 Rayleighs of the O II emission from the uppermost part of the ionosphere. The observation suggests that O+ ions convected from the cusp/cleft region exist over the polar ionosphere.