An evaporator evaporates a working fluid by heat from a battery. The evaporator includes at least one evaporation channel connected to the battery in a thermally conductive manner. The evaporator includes a supply channel connected to an upstream end of the evaporation channel, and supplies the working fluid in liquid phase from the supply channel to the evaporation channel. The evaporator includes an outflow channel connected with a downstream end of the evaporation channel, and discharges the working fluid. The outflow channel is disposed above the supply channel, and the supply channel is disposed at a position more insulated from the heat of the battery than the evaporation channel is.