PURPOSE: To detect the residual amount of an ink certainly and easily, by constituting an ink sub-tank from a transparent member.

CONSTITUTION: A sub-tank is constituted from a transparent member such as an acrylic resin member. As the transparent member, one undissolved in the solvent of an ink is pref. used and acrylic resin or styrenic resin is used. By the foregoing constitution, the residual amount of the ink in the sub-tank can be known extremely certainly and easily while the generation of ink non-emission can be previously removed.