To provide a cooling device capable of maintaining an evaporator side circuit even when an evaporator side pipe is closed by a maintenance open/close valve.

This cooling device comprises a primary side refrigerating circuit 1 for circulating ammonia refrigerant therein, a secondary side refrigerant circuit 2 for circulating carbon dioxide refrigerant therein, and a cascade condenser 3 for performing a heat exchange between the ammonia refrigerant and the carbon dioxide refrigerant. Even when the secondary refrigerant circuit 2 on the evaporator 23 side is closed and a refrigerant pressure in the evaporator 23 side circuit is abnormally increased, refrigerant can be discharged to the outside by safety valves 33 and 34 installed in the circuit on the evaporator 23 side. Thus, the circuit on the evaporator 23 side can be surely maintained.