To provide a magnetic shield room for reducing the magnetic field noise of a commercial power supply frequency entering the magnetic shield room, and its construction method.

In a magnetic shield room 1 where a ferromagnetic material is applied to such a structure as a floor 2, front and rear walls 3 and 4, left and right walls 6 and 7, and the ceiling 5 while the internal space is magnetically blocked, pairs of close circuited coils 11, 11'-13, 13' that oppose each other sandwiching the inner space in the direction of the three axes of the structure are arranged, and a magnetic noise in a commercial power supply frequency is reduced, thus reducing magnetic shield due to the application of the ferromagnetic material in the magnetic shield room. The method can also be applied to an existing magnetic shield room.