A method includes coupling a strain gauge to a tubular member, and positioning the tubular member in the wellbore such that the tubular member is placed under bending stress by a curvature or deviation in the wellbore. The method also includes measuring bend on the tubular member with the strain gauge in at least one plane and determining one or more of the magnitude or orientation of the curvature of the wellbore based on an output of the strain gauge.

A first point measurement control part (101) rotates a cylinder part (11a) of a cylindrical rotation part (11) to a predetermined reference cylindrical angle 1, rotates a columnar part (13a) of a mirror rotation part (13) to a predetermined reference mirror angle 1, makes the laser beam L irradiate, and measures a position of a predetermined first point A in a hollow from a reflection point R of the laser beam on the mirror (14). A first rotation control part (102) rotates the cylinder part (11a) from the reference cylindrical angle 1 to 180 degrees. A second rotation control part (103) rotates the columnar part (13a) from the reference mirror angle 1 to 180 degrees. A second point measurement control part (104) makes the laser beam L irradiate after the cylinder part (11a) is rotated by 180 degrees, and the columnar part (13a) is rotated by 180 degrees, and measures a position of a predetermined second point B in the hollow from the reflection point R of the laser beam L on the mirror (14). A correction control part (105) corrects a rotation operation of the cylinder part (11a) and a rotation operation of the columnar part (13a).

A first point measurement control part (101) rotates a cylinder part (11a) of a cylindrical rotation part (11) to a predetermined reference cylindrical angle 1, rotates a columnar part (13a) of a mirror rotation part (13) to a predetermined reference mirror angle 1, makes the laser beam L irradiate, and measures a position of a predetermined first point A in a hollow from a reflection point R of the laser beam on the mirror (14). A first rotation control part (102) rotates the cylinder part (11a) from the reference cylindrical angle 1 to 180 degrees. A second rotation control part (103) rotates the columnar part (13a) from the reference mirror angle 1 to 180 degrees. A second point measurement control part (104) makes the laser beam L irradiate after the cylinder part (11a) is rotated by 180 degrees, and the columnar part (13a) is rotated by 180 degrees, and measures a position of a predetermined second point B in the hollow from the reflection point R of the laser beam L on the mirror (14). A correction control part (105) corrects a rotation operation of the cylinder part (11a) and a rotation operation of the columnar part (13a).