Patent ID: 6848776

Claim:
An ink tank comprising: a main ink chamber being opened to the air; an ink outlet; a sub ink chamber including: a first sub ink chamber being formed between said main ink chamber and said ink outlet and allowing ink and air both coming from said main ink chamber to enter said first sub ink chamber; a second sub ink chamber, disposed between said first sub ink chamber and said ink outlet, for reserving said ink; and an ink passage for leading said ink and air bubbles, which are formed in said first sub ink chamber, from said first sub ink chamber to said second sub ink chamber; a detected portion, disposed at at least one of said ink passage and said second sub ink chamber, operable to optically detect whether said ink is used up on the basis of an amount of air flowed from said main ink chamber into said sub ink chamber; a main ink chamber side communication port communicatively connecting said main ink chamber with said sub ink chamber; a first filter mounted on said main ink chamber side communication port and having a first permeability for said air bubbles; an ink outlet side communication port communicatively connecting said second sub ink chamber to said ink outlet; and a second filter mounted on said ink outlet side communication port and having a second permeability for said air bubbles which is smaller than said first permeability.