In a cryostat having a vacuum container (6), a refrigerator (2) having an elongated part (2b, 2c) extending in the vacuum container and having a cooling section (36, 37), a cooled member (4, 5) cooled by the cooling section, and a thermal coupling member (21, 27) thermally coupling the cooling section (36, 37) with the cooled member (4, 5), the thermal coupling member includes a first thermal contactor (22, 28) thermally coupled to the cooling section, and a second thermal contactor (29) thermally coupled to the cooled member, the first and second contactors mating with each other. The mating surfaces of the first and second contactors are inclined, and one of the first and second contactors is mounted such that it can be moved. A resilient member presses said one of the contactors against the other contactor. The contact pressure at the mating surfaces is thereby kept substantially constant. Partitions may be provided to divide the space within the jacket into parts thereby to reduce heat infiltration by convection. A communication tube may be provided to connect the space within the jacket to a space in which evaporated cryogen gas is staying.