A tap phase detection method includes: acquiring a relation between a rotation angle and an existence of a screw thread by measuring a position of the screw thread of a tap with a sensor from a direction intersecting with an axial direction of the tap while rotating the tap; and detecting a phase of the tap based on the acquired relation between the rotation angle and the existence of the screw thread.

A tap phase detection method includes: acquiring a relation between a rotation angle and an existence of a screw thread by measuring a position of the screw thread of a tap with a sensor from a direction intersecting with an axial direction of the tap while rotating the tap; and detecting a phase of the tap based on the acquired relation between the rotation angle and the existence of the screw thread.