Abstract: An inkjet recording apparatus is provided, which comprises a sub-tank unit mounted on a carriage for supplying ink to an ink jet record head and an ink replenishment unit connected to a main tank installed on a housing by a duct and being able to be connected to and disconnected from the sub-tank unit. The sub-tank unit comprises an ink injection port and an exhaust port that are communicated with an ink storage chamber via self-seal type valve means, and a valve mechanism for opening and closing the exhaust port based on a liquid level of ink, wherein ink is supplied to the ink storage chamber by negative pressure from negative pressure generation means for sucking air through the exhaust port. Also provided is an ink droplet ejection capability recovery method for a recording head of an ink jet recording apparatus for determining an amount of ink remaining in the sub-tank unit, replenishing the sub-tank unit with ink from the main tank, and performing a recovery operation.