To provide a boring method capable of reducing the variation of the inner diameter of the hole of a workpiece after boring and improving the roundness of the hole of the workpiece after boring, and a boring device.

The boring method includes: a first step for boring a hole 2 of a workpiece 1 in a state in which the axis of the hole 2 of the workpiece 1 is does not incline relative to the axis of a working shaft 11; a second step for measuring the shape of the hole 2 of the workpiece 1 bored by the first step; a third step for calculating an inclination angle of the hole 2 of the workpiece 1 relative to the axis of the working shaft 11 on the basis of the measuring result by the second step; and a fourth step for boring a hole 2a of a new workpiece 1a. The boring by the fourth step is carried out in a state in which the axis of the hole 2a of the workpiece 1a is inclined by the inclination angle relative to the axis of the working shaft 11.