THREAD FORMING TAP

The present invention suppresses a reduction in durability and tool longevity by suppressing pressure on an leading flank during tapping machining. Provided is a thread forming tap wherein a screw thread 18 on a chamfer comprises an leading flank 18a, which is the advancing side thereof when screwed into a pilot hole in a workpiece 40, and a trailing flank 18b, which is the back side, and on the chamfer, the indentation depth Da into the workpiece 40 made by the leading flank 18a of the screw thread 18 is formed so as to be smaller than the indentation depth Db made by the trailing flank 18b of the screw thread 18. Therefore, during tapping machining, reaction force Fa from the workpiece 40 applied to the leading flank 18a to plastically deform the workpiece 40 is reduced more than the reaction force Fb from the workpiece 40 applied to the trailing flank 18b, and thus the reaction force Fb on the leading flank 18a is suppressed and a reduction in the durability and tool longevity of a thread forming tap 10 is suppressed.