Disclosed are a butt welding apparatus, a butt welding method, and a product manufactured by the butt welding method. Two electrode rollers (3, 4) are disposed on both the front and back sides of a thick sheet member (1) and on both the front and back sides of a thin sheet member (2) whose end surfaces (1A, 2A) are butted. The electrode rollers (3, 4) are applied with power, melt the butt portion (6) of the sheet members (1, 2) with electric resistance heat, and joint the butt portion. Further, the electrode rollers (3, 4) have a length bridging across the sheet members (1, 2) and are composed of first portions (3A, 4A) arranged as small diameter portions on the side of the thick sheet member (1) and second portions (3B, 4B) arranged as large diameter portions on the side of the thin sheet member (2). The first portions (3A, 4A) come into contact with the thick sheet member (1) and presses it before the second portions (3B, 4B) come into contact with the thin sheet member (2). Thus, the end surface (1A) of the thick sheet member (1) swells and deforms toward the thin sheet member (2) and reliably comes into contact with the end surface (2A) of the thin sheet member (2). As a result, power is applied between the end surfaces (1A, 2A) even if the end surfaces (1A, 2A) are not finished by polishing and the like.