A welding method comprising: a step of preparing a first base material and a second base material; a step of disposing the first base material and the second base material in a manner such that a first end face of the first base material and a second end face of the second base material face each other; and a step of welding the first base material and the second base material together using GMA welding so that the first end face and the second end face are joined together, wherein an arc is formed between a welding wire and each of the first base material and the second base material and a molten region is formed at the first base material and the second base material by heat of the arc, so that the first base material and the second base material are welded together in the step of welding the first base material and the second base material together, wherein the arc is formed in a state where the welding wire penetrates into a region surrounded by the molten region, so that the molten region is formed to pierce through the first base material and the second base material in a thickness direction in the step of welding the first base material and the second base material together, wherein a mean current is equal to or larger than 300 A, a feed speed of the welding wire is equal to or higher than 30 m/min in the step of welding the first base material and the second base material together, and the first base material and the second base material are welded together in a state where voltage reduction with respect to current increase of 100 A is equal to or larger than 4 V and equal to or smaller than 20 V in the step of welding the first base material and the second base material together. a step of preparing a first base material and a second base material; a step of disposing the first base material and the second base material in a manner such that a first end face of the first base material and a second end face of the second base material face each other; and a step of welding the first base material and the second base material together using GMA welding so that the first end face and the second end face are joined together, wherein an arc is formed between a welding wire and each of the first base material and the second base material and a molten region is formed at the first base material and the second base material by heat of the arc, so that the first base material and the second base material are welded together in the step of welding the first base material and the second base material together, wherein the arc is formed in a state where the welding wire penetrates into a region surrounded by the molten region, so that the molten region is formed to pierce through the first base material and the second base material in a thickness direction in the step of welding the first base material and the second base material together, wherein a mean current is equal to or larger than 300 A, a feed speed of the welding wire is equal to or higher than 30 m/min in the step of welding the first base material and the second base material together, and the first base material and the second base material are welded together in a state where voltage reduction with respect to current increase of 100 A is equal to or larger than 4 V and equal to or smaller than 20 V in the step of welding the first base material and the second base material together.