To measure and observe size of an extremely minute gap between two objects which contact each other directly or via lubricant, etc. and the minute surface shape of both objects near a contact part of them.

A contact part of two objects 4A, 4B is irradiated with X-rays at an incident angle that an angle to a tangent plane of the contact part is equal to or less than the total reflection critical angle, passage X-rays, diffraction and scattered X-rays, characteristic X-rays, etc. to be emitted from the contact part to the opposite side are detected by a position sensitive type two-dimensional X-ray detector 5. A two-dimensional X-ray intensity distribution creation part 61 creates a two-dimensional X-ray intensity distribution image by a detection signal from the X-ray detector 5, and an analysis processing part 62 extracts only a plurality of pixels included in a detection window set according to, for example, kinds (such as points, lines) of contact in the image to integrate X-ray intensity of the pixels. Then, size of a minute gap existing at the contact part is calculated based on the integrated X-ray intensity, an intensity pattern to be calculated from the two-dimensional X-ray intensity distribution image is simultaneously analyzed to estimate the surface shape.