Higher-precision measurement is achieved by an optical inner surface measuring device configured to cause a probe to enter into the inner peripheral surface or deep hole of a target object, capture and observe reflection light from the inner surface in a three-dimensional manner, and measure the accuracy of the target object. In a structure including an optical fiber built into a tube, a light path conversion unit arranged at a leading end side of the optical fiber, and a motor configured to rotationally drive the light path conversion unit, a unit for measuring the amount of runout of a rotation shaft unit of the motor is provided. Shape data on the inner peripheral surface of a target object is obtained by calculating at a computer reflection light from the target object, and is modified by displacement amount data from a displacement measurement unit to realize high-precision measurement with no measurement error resulting from runout and rotational vibration of the rotation shaft of the motor.