Inner Circumferential Length Measuring Device for Circular Member

An inner circumferential length measuring device for a circular member, comprising:

• a support on which the circular member is placed;
• a two-dimensional sensor disposed allowing for movement relative to the support;
• a rotation driving mechanism configured to rotate the two-dimensional sensor;
• and
• a calculation unit configured to receive measurement data from the two-dimensional sensor;
• the two-dimensional sensor being disposed at a predetermined measurement position facing an inner circumferential surface of the circular member placed flat in an unrestrained state on the support;
• by the two-dimensional sensor being rotated about a predetermined position inward of the circular member via the rotation driving mechanism, a separation distance from the two-dimensional sensor to the inner circumferential surface being measured by the two-dimensional sensor in a non-contact state with the circular member in a range of an entire circumference of the circular member;
• and
• the calculation unit calculating an inner circumferential length of the circular member based on the separation distance measured and a distance from the predetermined position to the two-dimensional sensor in a plan view.