An ink jet unit to which an ink container is detachably mountable, and which is further mountable to an ink jet recording apparatus so as to effect ink jet recording. The ink jet unit includes an ink jet head for ejecting ink for recording, an ink supply tube for receiving ink from the ink container and being provided at a bottom portion of the ink jet unit in fluid communication with the ink jet head, and an opening for permitting mounting of the ink container thereto. The opening is formed continuously, in such sides of the ink jet unit as take top and front positions when the ink jet unit is mounted to the ink jet recording apparatus. A cover is provided, at the top side of the ink jet unit. The cover includes at an inside thereof a substantially non-elastic material provided at least at an inner corner between the top side and a rear side of the ink jet unit, and further includes an inclined portion which increases resistance against insertion of the ink container through the opening during mounting of the ink container as well as a substantially horizontal portion, all for urging the ink container downwardly to mount the ink container for fluid communication with the ink supply tube.