A liquid supply unit configured to be mountable on a liquid supply unit mounting structure, the liquid supply mounting structure having a first liquid introducing part, a second liquid introducing part, a third liquid introducing part and a projection which is located between the first liquid introducing part and the second liquid introducing part and is located between the third liquid introducing part and a part between the first liquid introducing part and the second liquid introducing part, the liquid supply unit comprising: a first liquid supply port configured to be connectable with the first liquid introducing part such as to supply a first liquid to the first liquid introducing part; a second liquid supply port configured to be connectable with the second liquid introducing part such as to supply a second liquid to the second liquid introducing part; a third liquid supply port configured to be connectable with the third liquid introducing part such as to supply a third liquid to the third liquid introducing part; a first wall configured to have the first liquid supply port, the second liquid supply port, the third liquid supply port and a groove; a second wall opposed to the first wall; a third wall arranged to intersect with the first wall and the second wall; a fourth wall arranged to intersect with the first wall and the second wall and opposed to the third wall; a fifth wall arranged to intersect with the first wall and the second wall; and a sixth wall arranged to intersect with the first wall and the second wall and opposed to the fifth wall, wherein in a plan view of the liquid supply unit in a direction from the first wall toward the second wall, the first liquid supply port is located between the fifth wall and the sixth wall, the second liquid supply port is located between the first liquid supply port and the sixth wall, characterized in that the groove is formed between the first liquid supply port and the second liquid supply port and is extended from between the first liquid supply port and the second liquid supply port toward the third liquid supply port, such as to allow the projection to be inserted therein, the groove is extended from the fourth wall toward the third wall, and the third liquid supply port is located between the groove and the third wall. a first liquid supply port configured to be connectable with the first liquid introducing part such as to supply a first liquid to the first liquid introducing part; a second liquid supply port configured to be connectable with the second liquid introducing part such as to supply a second liquid to the second liquid introducing part; a third liquid supply port configured to be connectable with the third liquid introducing part such as to supply a third liquid to the third liquid introducing part; a first wall configured to have the first liquid supply port, the second liquid supply port, the third liquid supply port and a groove; a second wall opposed to the first wall; a third wall arranged to intersect with the first wall and the second wall; a fourth wall arranged to intersect with the first wall and the second wall and opposed to the third wall; a fifth wall arranged to intersect with the first wall and the second wall; and a sixth wall arranged to intersect with the first wall and the second wall and opposed to the fifth wall, wherein in a plan view of the liquid supply unit in a direction from the first wall toward the second wall, the first liquid supply port is located between the fifth wall and the sixth wall, the second liquid supply port is located between the first liquid supply port and the sixth wall, characterized in that the groove is formed between the first liquid supply port and the second liquid supply port and is extended from between the first liquid supply port and the second liquid supply port toward the third liquid supply port, such as to allow the projection to be inserted therein, the groove is extended from the fourth wall toward the third wall, and the third liquid supply port is located between the groove and the third wall.