To provide a cooling system capable of cooling a heat load in a normal state and heating the heat load up to its operating temperature and normally operating it when the temperature of the heat load is lower than its normally operating temperature, and even when the load is small and the temperature thereof does not rise by self-heat generation upon turning on it.

In a cooling system for cooling a device (heat load) with high heat generation by using a vapor cycle, the control valve 24 of a pipeline for connecting the outlet of the compressor 3 of a first heat transfer medium circulating passage 10 in which refrigerant gas circulates to the inlet of a second heat exchanger 2 is opened to form the circulating passage of high temperature gas. A control valve 22 is controlled so that high temperature gas bypasses a first heat exchanger to form the circulating passage of high temperature gas. A third heat transfer medium as a medium performing a heat exchange between the heat load and itself is heated by an evaporator 2. The heat load can be heated by the third heat transfer medium thus heated.