An ink supply unit is provided and includes an ink container, and a cap fittable to the ink container and having an opening, a valve body, and an elastic body, an ink tank that holds the ink container fitted with the cap at a cap-side part of the container, a pivotable lever disposed on the ink tank pivotably around a pivot axis that is a pivoting center; an anti-rotation mechanism configured to restrict relative rotations of the ink container and of the cap to the ink tank, a conversion mechanism configured to convert the pivoting motion of the pivotable lever into linear motions of the ink container and of the cap in a direction along the pivot axis, and a valve-opening projection that presses the valve body toward an opening position when the cap is drawn nearer to the ink tank by the linear motion of the cap.