Liquid supply unit and liquid injection device

A liquid supply unit for supplying predetermined liquid from a liquid storage container storing the liquid to a liquid injection head for injecting the liquid, comprising:

• a first chamber communicating with the liquid storage container;
• a second chamber arranged downstream of the first chamber in a liquid supply direction and communicating with the liquid injection head;
• a wall portion including a communication opening allowing communication between the first chamber and the second chamber;
• an opening/closing member arranged to be able to open and close the communication opening from the second chamber side and configured to change a posture between a closing posture for closing the communication opening and an opening posture for opening the communication opening;
• a flexible film member defining a side surface of the second chamber facing the communication opening and configured to be displaced based on a pressure change of the second chamber;
• and
• a transmitting member configured to transmit a displacement force of the flexible film member to the opening/closing member in a direction opposite to a displacement direction of the flexible film member, the transmitting member transmitting the displacement force to the opening/closing member to set the opening/closing member to the opening posture when the second chamber is set to a negative pressure exceeding a predetermined threshold value as the liquid in the second chamber decreases and transmitting the displacement force to the opening/closing member to set the opening/closing member to the closing posture according to a displacement of the flexible film member when the second chamber is pressurized.