Provided is a local heatsink welding device and a method of welding using the same. The local heatsink welding device includes a welding torch disposed above welds of two pieces of a base metal placed in contact with each other to be welded, the welding torch welding the pieces of the base metal by melting a welding wire on the welds of the base material and fusing the pieces together; and a cooling unit disposed to be able to spray a low-temperature fluid from the sides of the welding torch, the cooling unit cooling at least a portion of a heat-affected zone formed around the outside of a fusion zone in which the base material is molten during welding. The local heatsink welding device can improve mechanical properties such as mechanical strength and fracture toughness of welds such as a pressure vessel for a power plant by suppressing the formation of carbide coarsening on a non-transformation heat-affected zone during welding, without adding a new heat treatment process to the production of steel for the pressure vessel.