This heat exchanger 18 is provided with: a low temperature side flow path 32 in which liquid helium at a low temperature flows; a high temperature side flow path 30 in which liquid helium at a high temperature flows; and a heat transfer part 36 which transfers heat from the high temperature side flow path 30 to the low temperature side flow path 32. The heat transfer part 36 comprises: a partition member which separates the high temperature side flow path 30 and the low temperature side flow path 32 from each other; and a thermal resistance reduction part 40 which reduces the thermal resistance between the partition member and the liquid helium. The thermal resistance reduction part 40 comprises: a porous body that has nanometer-sized pores; and metal fine particles which have a higher thermal conductivity than the porous body.