Joint welded by electron beam with excellent unsusceptibility to brittle fracture

High-strength steel plates having a yield strength of 355 MPa or higher and a thickness larger than 50 mm are butt-welded by electron beam welding to form a welded joint having a sufficiently high fracture toughness value dc. The butt-welded joint has been regulated so that the hardness of the weld metal part is 110-220% based on the hardness of the base plates and the width of the weld metal part is up to 20% of the thickness of the base plates. Preferably, the weld metal of the welded joint has been regulated so that the amount of oxygen contained therein is 20 ppm or larger and the number of oxide particles having a diameter of 2.0 [mu]m or larger present therein is up to 10 per mm. Alternatively, the weld metal of the welded joint has preferably been regulated so as to have a nickel content which is 1-4 mass% and is higher by at least 0.2 mass% than that in the base plates. When the base plates are a steel material having a nickel content of 2.5 mass% or higher, the nickel content in the weld metal of the welded joint has preferably been regulated to 4-8 mass%, excluding 4 mass%.