PURPOSE: To obtain a shape measuring instrument which can accurately obtain an object shape without any contact.

CONSTITUTION: X, Y, and Z sliders are provided with a measurement head housing a probe, a rotator 101, and a drive part 102 for rotating the rotator 101, the flux of light from a light source means 1 is applied to an object to be measured via a probe, and the flux of light from the object to be measured is received by a light reception means 11 via the probe. When measuring the shape of the object to be measured by utilizing a signal from the light reception means 11, a reference mirror 4 and a first light reception element 11 are provided at the drive part 102, a measurement mirror 9 and a second light reception element 8 are provided at the rotator 101, and an interference length measuring instrument is constituted by utilizing flux of light via the reference mirror 4 and the measurement mirror 9. An interference signal obtained by the interference length measuring instrument is detected by the first light reception element 11 to obtain the rotary motion error in the rotary shaft direction of the rotator 101 and an incidence position onto a specific surface of flux of light via the interference length measuring instrument is detected by the second light reception element 8, thus obtaining the rotary motion error in the radius direction of the rotator 101.