A liquid supply unit for injecting 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 in the communication opening, a posture of the opening/closing member being changed between a closing posture for closing the communication opening and an opening posture for opening the communication opening; a biasing member configured to bias the opening/closing member in a direction toward the closing posture; a pressing member capable of pressing the opening/closing member in a direction toward the opening posture; and a flexible film member configured to be displaced based on a negative pressure generated as the liquid in the second chamber decreases and transmits a displacement force thereof to the pressing member, the flexible film member partially constituting the second chamber; wherein the pressing member: includes a pivot point, a pressure receiving portion configured to receive the displacement force from the flexible film member, a pressing portion configured to press the opening/closing member against a biasing force of the biasing member and the pressing member including a flat plate portion having the pivot point arranged on one end side and rotatable about the pivot point; the pressure receiving portion is set at a predetermined position of the flat plate portion, the pressing portion is set between the pressure receiving portion and the pivot point on the flat plate portion, the pressing member rotates about the pivot point when the pressure receiving portion receives the displacement force, the pressing portion pressing the opening/closing member by the rotation of the pressing member, the opening/closing member is link-connected to the flat plate portion at the pressing portion, and the biasing member biases the opening/closing member in the direction toward the closing posture by biasing a biased portion set at a position corresponding to the pressure receiving portion on the flat plate portion. 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 in the communication opening, a posture of the opening/closing member being changed between a closing posture for closing the communication opening and an opening posture for opening the communication opening; a biasing member configured to bias the opening/closing member in a direction toward the closing posture; a pressing member capable of pressing the opening/closing member in a direction toward the opening posture; and a flexible film member configured to be displaced based on a negative pressure generated as the liquid in the second chamber decreases and transmits a displacement force thereof to the pressing member, the flexible film member partially constituting the second chamber; wherein the pressing member: includes a pivot point, a pressure receiving portion configured to receive the displacement force from the flexible film member, a pressing portion configured to press the opening/closing member against a biasing force of the biasing member and the pressing member including a flat plate portion having the pivot point arranged on one end side and rotatable about the pivot point; the pressure receiving portion is set at a predetermined position of the flat plate portion, the pressing portion is set between the pressure receiving portion and the pivot point on the flat plate portion, the pressing member rotates about the pivot point when the pressure receiving portion receives the displacement force, the pressing portion pressing the opening/closing member by the rotation of the pressing member, the opening/closing member is link-connected to the flat plate portion at the pressing portion, and the biasing member biases the opening/closing member in the direction toward the closing posture by biasing a biased portion set at a position corresponding to the pressure receiving portion on the flat plate portion. includes a pivot point, a pressure receiving portion configured to receive the displacement force from the flexible film member, a pressing portion configured to press the opening/closing member against a biasing force of the biasing member and the pressing member including a flat plate portion having the pivot point arranged on one end side and rotatable about the pivot point; the pressure receiving portion is set at a predetermined position of the flat plate portion, the pressing portion is set between the pressure receiving portion and the pivot point on the flat plate portion, the pressing member rotates about the pivot point when the pressure receiving portion receives the displacement force, the pressing portion pressing the opening/closing member by the rotation of the pressing member, the opening/closing member is link-connected to the flat plate portion at the pressing portion, and the biasing member biases the opening/closing member in the direction toward the closing posture by biasing a biased portion set at a position corresponding to the pressure receiving portion on the flat plate portion.