PROBLEM TO BE SOLVED: To enable safe measurement by reducing shock to a brain surface in the method where state change of brain tissue or the like is measured by using light under an environment where the brain surface or the dura mater is exposed.SOLUTION: A shock absorber for optical brain surface measurement which is used for optical topography measurement on a brain surface includes: a sheet part 101 which is composed of flexible material and whose surface contacting with the brain surface is plane a light-irradiation/detection hole 102 which is disposed on the sheet part and is used for emitting or detecting light. The light-irradiation/detection hole is smaller than an irradiation surface of a light irradiation apparatus or a detection surface of a light detection apparatus.
