[Problem] To enable stable measurement unaffected by surface shape or roughness, prevent the effects of heat generated by a motor housed in a measurement probe, eliminate the effects of vibration or deviation of bearings of the motor, and correctly perform accurate measurements of high-precision inside diameters and inner peripheral surfaces in an optical inner-surface measurement device. [Solution] The present invention has an optical fiber housed in a tube, and at least one optical path conversion means provided to the distal-end part of the optical fiber, and also has a motor for rotatably driving the optical path conversion means, the motor being provided inside the tube. A gas drawn in from a location further toward the distal-end side than the motor passes through the interior of the tube and is exhausted from a location further to the front side from the motor. The present invention is configured such that a hard translucent pipe is attached to the distal-end part of the tube, the translucent pipe is inserted into the inside diameter of a to-be-measured object, a light beam guided through the optical fiber is emitted from the optical path conversion means and radiated on the inner peripheral surface of the to-be-measured object through the translucent pipe, and light reflected from the inner peripheral surface is detected through the translucent pipe.Le problème décrit par la présente invention est de permettre une mesure stable non affectée par la forme ou la rugosité de surface, et empêche les effets de la chaleur générée par un moteur logé dans une sonde de mesure, éliminent les effets de vibration ou de déviation des paliers du moteur, et réalisent correctement des mesures précises de diamètres intérieurs de haute précision et de surfaces périphériques intérieures dans un dispositif de mesure optique de surface intérieure. [Solution] la présente invention a trait à une fibre optique logée dans un tube, et au moins un moyen de conversion de chemin optique
