There is provided a cassette for a fluid infusion pump that can reliably switch between a free flow state and an anti-free flow state and easily address an infusion by free fall, and has extremely small number of components and causes few malfunctions. A cassette 1 mounted to a fluid infusion tube 2 and installed in a fluid infusion pump includes a clamp portion 12 that releasably clamps the fluid infusion tube 2 to block a liquid flow in the fluid infusion tube 2. The clamp portion 12 has a pressing portion 16 provided so as to be freely pressed on the fluid infusion tube 2, a biasing member 15 that biases the pressing portion 16 in a pressing direction on the fluid infusion tube 2, and a pressing release portion that releases pressing by the pressing portion 16 by a pressing operation against a biasing direction of the biasing member 15. The biasing member 15 is provided movably between a position for biasing the pressing portion 16, and a position for releasing bias on the pressing portion 16.
