Liquid supplying apparatus and image forming apparatus

A liquid supplying apparatus comprising:

• a replaceable ink cartridge used as a main tank storing ink as a recording liquid;
• a sub-tank to which the ink cartridge is connected via a supplying path and the ink inside the ink cartridge is supplied;
• nozzles from which the recording liquid stored in the sub-tank is ejected;
• and
• an ink cartridge installation part detachably accommodating the ink cartridge,
• the ink cartridge having
• a first ink container that stores the ink and freely increases and decreases a volume thereof in accordance with a storing amount of the ink and
• a second ink container enclosing the first ink container,
• the first ink container having
• a holding member having a position thereof lowered in accordance with a remaining amount of the ink,
• the second ink container having
• an ink cartridge replacement operating member capable of being opened in a direction so as to outwardly protrude from a position adjacent to a side wall of the second ink container to a position allowing an operation on the ink cartridge from an outside of the ink cartridge installation part,
• a biasing unit that biases the operating member in the direction where the operating member is opened, and
• a locking unit that is provided at the side wall of the second ink container and fixes the operating member at the position adjacent to the side wall of the second ink container against the biasing unit,
• the locking unit engaging the operating member until the remaining amount of the ink inside the first ink container is below a prescribed value and the holding member engages the locking unit,
• the locking unit releasing engagement of the operating member when the remaining amount of the ink inside the first ink container is below the prescribed value and the holding member engages the locking unit,
• the operating member protruding from the ink cartridge installation part and being opened to the position allowing the operation on the ink cartridge from the outside when the engagement with the locking unit is released. 10