PURPOSE: To enlarge the measuring visual field and enable measurement to be performed even if there is a shieding obstacle between the rotating body to be inspected and an erected prism, by providing the first and second optical systems each making one of the light halved by a beam splitter incident on an erected prism as an object light.

CONSTITUTION: With an erected prism 11 rotated, the laser beam from a laser apparatus 2 is shut off by a light-screening plate 3, and light-screening plates 7 and 17 are set at solid-line positions. The pulse laser beam from a pulse laser apparatus 19 is halved by a beam splitter 4. The transmitted light passes through the first optical system comprising a beam splitter 6 and a rectangular prism 8 and irradiates an impeller 1 from an oblique direction. Said light is reflected therefrom and reaches a photographic plate 12a for holography as an object light. Next, when the light- screening plates 7 and 17 are moved to the broken-line positions, the second-shot pulse laser beam passes through the second optical system comprising the beam splitter 6 and a rectangular prism 18 and irradiates the impeller 1 from an oblique direction, and is reflected therefrom to become an object light.