To provide a two-dimensional accurate measuring instrument for coming flying direction of gamma ray which can obtain the accurate positional information on a gamma ray and is improved in resolution.

The measuring instrument is provided with a converter 2 which is constituted by alternately laminating grid materials 4 each having many through holes 7 divided from each other by partition walls 4A and insulating materials 5 upon another. In each through hole 7, a hollow channel 8 is formed for passing electrons. The instrument is also provided with a two-dimensional electronic measuring instrument 3 on the bottom side of the converter 2.