To provide an insulated box for a boat which is excellent in cooling capacity and can always conduct stable cooling and which is small in size and light in weight and realizes power-saving.

The main body 20 of a insulated box which is fitted to the hull 100 of a boat and composed of a vessel 21 and a cover 22, a Peltier module of which a heat absorbing surface is directed inside and a heat emitting surface outside and which is fitted to a part of the vessel 21, and a radiating means 30 which is so fitted to the heat emitting surface of the Peltier module as to be in contact with or in proximity to this surface, are provided. The radiating means 30 is made a water passing means 30 having a water supply port 31 and a water discharge port 32. In addition to this, moreover, a pump 10 supplying the water supply port 31 with water for cooling from a water source W under the hull and a draining port 40 draining, outside the hull, the water for cooling discharged from the water discharge port 32 are provided.