To provide a thermosiphon capable of facilitating manufacture and attaining low cost, having excellent pressure resistance and preventing the circulation of operating fluid from being obstructed.

A condenser 3 includes a condensing part 4 formed of an extruded material having a plurality of pores 7, a branch part 5 provided on the upstream side of the pore 7 of the condensing part 4 for guiding gaseous working fluid returned from a gas pipe 12 to each pore 7 of the condensing part 4, and a collecting part 6 provided on the downstream side of the pore 7 of the condensing part 4 for collecting the working fluid condensed in the pores 7 of the condensing part 4 and guiding the same to a liquid pipe 9. The gas pipe 12 is connected to the upper side of the branch part 5, and the liquid pipe 9 is connected to the lower side of the collecting part 6.