Butterfly valve and manufacturing method therefor

Provided is a butterfly valve (1) that is positioned by two pins (5), which are provided on a circular valve (3), when the circular valve (3) is inserted into a slit (4) in a shaft (2). In addition, a first surface (3a) of the circular valve (3) is made to abut the shaft (2) in an outlet-side opening (4b) using a pressing-down fixing tool (6) when laser welding is to be performed and the part where abutting occurs is laser welded. Consequently, a sufficiently strong first welded section (7) that does not contain a gap (4c) is obtained and the shaft (2) and the circular valve (3) are joined to each other in a state where central axes S1, S2 of the shaft (2) and the circular valve (3) are substantially aligned. Furthermore, by forming laser irradiation heat input sections (9, 10) at places on the circular valve (3) opposing (right in the back of) the first welded section (7) and a second welded section (8), the same degree of flatness as before the welding can be obtained for the circular valve (3) and the amount of leakage when the circular valve (3) is fully closed can be reduced.