A refrigerant-filled thermosiphon comprising: a condensing member for condensing the refrigerant, the condensing member being provided on a heat-absorbing section of a Stirling cycle cooler; and a pipe formed in an annular shape and connected to the condensing member, the pipe being arranged around a container so as to absorb a heat of the container, wherein the pipe comprises two paths, each path being arranged so as to extend downwardly along a half-periphery of the container. By employing this structure, the inclination angle of each path can be increased, and thus the flow of the liquefied refrigerant in the pipe can not be easily prevented even if a cooling box equipping the thermosiphon tilts in some degree.