A welded structure, in which a second tubular member is welded to an inner circumference of a first tubular member made of metal, the second tubular member being made of metal and having an outer diameter smaller than an inner diameter of the first tubular member, includes welded portions at which a portion of the first tubular member and a portion of the second tubular member are melted and solidified, a surface melted and solidified from an inner circumferential surface side of the first tubular member toward an end surface of the second tubular member forms a smoothly-continuous curved surface, and the first and the second tubular members are bonded to each other. A portion of each of the welded portions is located on an outside of a projection region obtained by projecting the second tubular member onto an outer surface of the first tubular member.
