INSIDE-DIAMETER MEASUREMENT DEVICE

The invention relates to an inner diameter measuring device, having a non-contact measuring unit (3) and a contact measuring unit (4) arranged along the same center line, wherein the non-contact measuring unit comprises an image pickup unit (6) arranged on the center line, a laser beam emitting unit (7), and a laser beam diffusing unit (9) having a cone mirror, wherein a laser beam projected from the laser beam emitting unit to the cone mirror is reflected over a total circumference by the cone mirror, the image pickup unit takes an optical ring which is formed by projecting the reflected laser beam to an inner surface of a hollow portion, at least one of an inner diameter or a shape of the inner surface is measured based on an image picked up, and wherein the contact measuring unit comprises a contact measuring head (42) and a circulation unit (41) for circulating the contact measuring head around the center line, wherein the contact measuring head has a contact measuring unit having a contact at a forward end and for detecting a displacement of the contact, an advancing/retreating unit for advancing and retreating the contact measuring unit in radial direction, and a scale unit for measuring an advancing/retreating distance of the contact measuring unit.