A liquid supply system comprising: a first vessel for housing ultracold liquid such as liquid nitrogen and liquid helium; a second vessel disposed in the liquid housed in the first vessel to take in the liquid and to deliver the taken-in liquid into a supply passage communicating with an outside of the liquid supply system; a first bellows disposed to enter the second vessel; and a shaft formed to be reciprocated by a driving source to cause the first bellows to expand and contract, wherein an outside of the first bellows serves as a first pump chamber provided with a first intake port for taking the liquid in the first vessel into the first pump chamber and a first delivery port for delivering the taken-in liquid from inside the first pump chamber into the supply passage, an inside of the first bellows serves as a second pump chamber formed as sealed space and provided with a second intake port for taking the liquid in the first vessel into the second pump chamber and a second delivery port for delivering the taken-in liquid from inside the second pump chamber into the supply passage, characterized in that a sealed space (R1, R2) is formed through which the shaft extending from outside the first vessel to reach the first bellows is inserted; an inside of the sealed space is evacuated or filled with gas, or a layer of the liquid and a layer of gas are formed in the sealed space, wherein when a layer of the liquid and a layer of gas are formed in the sealed space, a branch passage branching off the supply passage is connected to the sealed space to form a buffer structure for buffering pressure variation of the liquid supplied through the supply passage; and the sealed space (R1, R2) is formed by a pipe portion through which the shaft is inserted, a small second bellows provided to a lower end portion of the pipe portion and a small third bellows provided to an upper end portion of the pipe portion, both the small bellows (162, 163) being configured to expand and contract as the shaft reciprocates and having smaller outer diameters than the first bellows. a first vessel for housing ultracold liquid such as liquid nitrogen and liquid helium; a second vessel disposed in the liquid housed in the first vessel to take in the liquid and to deliver the taken-in liquid into a supply passage communicating with an outside of the liquid supply system; a first bellows disposed to enter the second vessel; and a shaft formed to be reciprocated by a driving source to cause the first bellows to expand and contract, wherein an outside of the first bellows serves as a first pump chamber provided with a first intake port for taking the liquid in the first vessel into the first pump chamber and a first delivery port for delivering the taken-in liquid from inside the first pump chamber into the supply passage, an inside of the first bellows serves as a second pump chamber formed as sealed space and provided with a second intake port for taking the liquid in the first vessel into the second pump chamber and a second delivery port for delivering the taken-in liquid from inside the second pump chamber into the supply passage, characterized in that a sealed space (R1, R2) is formed through which the shaft extending from outside the first vessel to reach the first bellows is inserted; an inside of the sealed space is evacuated or filled with gas, or a layer of the liquid and a layer of gas are formed in the sealed space, wherein when a layer of the liquid and a layer of gas are formed in the sealed space, a branch passage branching off the supply passage is connected to the sealed space to form a buffer structure for buffering pressure variation of the liquid supplied through the supply passage; and the sealed space (R1, R2) is formed by a pipe portion through which the shaft is inserted, a small second bellows provided to a lower end portion of the pipe portion and a small third bellows provided to an upper end portion of the pipe portion, both the small bellows (162, 163) being configured to expand and contract as the shaft reciprocates and having smaller outer diameters than the first bellows.