An image forming apparatus includes an image forming part to form an image by injecting a liquid. A waste liquid tank is detachably attached to the image forming apparatus to store a waste liquid discharged from the image forming part. The waste liquid tank has a memory element to store identification information A and waste liquid amount information B. A memory unit stores identification information C and waste liquid amount information D. A control unit determines a current amount of the waste liquid currently retained in the waste liquid tank at a predetermined timing in accordance with the identification information A and the waste liquid amount information B stored in the memory element and the identification information C and the waste liquid amount information D stored in the memory unit, and updates the current amount of the waste liquid in accordance with a subsequent operation of the image forming part.