A liquid tank which is mounted to a carriage including a liquid ejection head, the liquid tank comprising: a liquid supply portion which includes a liquid supply port adapted to receive a liquid introduction needle included in the liquid ejection head; a first liquid chamber configured to store a liquid to be supplied to the liquid supply portion; a liquid communication flow path through which the first liquid chamber is in fluid communication with the liquid supply portion, the liquid communication flow path forming a flow path that is upwardly convex in a mounting state where the liquid tank is mounted to the carriage; and an air communication flow path through which the first liquid chamber is in communication with the liquid supply portion, the air communication flow path connected to the first liquid chamber in a position higher than a position of connection of the liquid communication flow path and the first liquid chamber in the mounting state, wherein in a direction of flow of the liquid from the liquid tank toward the liquid ejection head, the liquid communication flow path includes: an upstream end which is connected to the first liquid chamber; a rising flow path which is located on a downstream side with respect to the upstream end and which extends upward in the mounting state; a lowering flow path which is located on the downstream side with respect to the rising flow path and which extends downward in the mounting state; and a downstream end which is located on the downstream side with respect to the lowering flow path and which is connected to the liquid supply portion, and in the mounting state, the liquid supply portion is located lower than the downstream end and extends downward toward the liquid supply port; the liquid tank further comprising: a second liquid chamber configured to store the liquid to be supplied to the first liquid chamber; a connection flow path adapted to connect the first liquid chamber and the second liquid chamber together and which is configured to supply the liquid in the second liquid chamber to the first liquid chamber; characterized by further comprising: a liquid filling portion through which the liquid is filled into the second liquid chamber; and an atmosphere communication portion which makes the second liquid chamber communicate with the atmosphere. a liquid supply portion which includes a liquid supply port adapted to receive a liquid introduction needle included in the liquid ejection head; a first liquid chamber configured to store a liquid to be supplied to the liquid supply portion; a liquid communication flow path through which the first liquid chamber is in fluid communication with the liquid supply portion, the liquid communication flow path forming a flow path that is upwardly convex in a mounting state where the liquid tank is mounted to the carriage; and an air communication flow path through which the first liquid chamber is in communication with the liquid supply portion, the air communication flow path connected to the first liquid chamber in a position higher than a position of connection of the liquid communication flow path and the first liquid chamber in the mounting state, wherein in a direction of flow of the liquid from the liquid tank toward the liquid ejection head, the liquid communication flow path includes: an upstream end which is connected to the first liquid chamber; a rising flow path which is located on a downstream side with respect to the upstream end and which extends upward in the mounting state; a lowering flow path which is located on the downstream side with respect to the rising flow path and which extends downward in the mounting state; and a downstream end which is located on the downstream side with respect to the lowering flow path and which is connected to the liquid supply portion, and an upstream end which is connected to the first liquid chamber; a rising flow path which is located on a downstream side with respect to the upstream end and which extends upward in the mounting state; a lowering flow path which is located on the downstream side with respect to the rising flow path and which extends downward in the mounting state; and a downstream end which is located on the downstream side with respect to the lowering flow path and which is connected to the liquid supply portion, and in the mounting state, the liquid supply portion is located lower than the downstream end and extends downward toward the liquid supply port; a second liquid chamber configured to store the liquid to be supplied to the first liquid chamber; a connection flow path adapted to connect the first liquid chamber and the second liquid chamber together and which is configured to supply the liquid in the second liquid chamber to the first liquid chamber; characterized by further comprising: a liquid filling portion through which the liquid is filled into the second liquid chamber; and an atmosphere communication portion which makes the second liquid chamber communicate with the atmosphere. a liquid filling portion through which the liquid is filled into the second liquid chamber; and an atmosphere communication portion which makes the second liquid chamber communicate with the atmosphere.