A working medium contains (E)-1,3,3,3-tetrafluoropropene, (Z) 1-chloro-2,3,3,3-tetrafluoropropene, and 1,1,1,2-tetrafluoroethane, wherein, with respect to a total content of the (E)-1,3,3,3-tetrafluoropropene, the (Z) 1-chloro-2,3,3,3-tetrafluoropropene, and the 1,1,1,2-tetrafluoroethane, a content of the 1,1,1,2-tetrafluoroethane is 14.5% by
mass or less, a content of the (Z) 1-chloro-2,3,3,3-tetrafluoropropene is 10.0% by
mass or less, and a content of the (E)-1,3,3,3-tetrafluoropropene is 75.5% by
mass or more.