In a refillable ink cartridge having an ink supply opening portion that is hermetically sealed with a sealing member, leakage of ink out of the cartridge due to a decrease in the sealing property of the sealing member is prevented. The sealing member, which is elastically deformable, is penetrated by a needle-shaped member when refilling the cartridge with ink via the ink supply opening portion. The ink supply opening portion is covered with a protection member including a projecting portion for hermetically sealing the ink supply opening portion outside the sealing member.