To provide an optical detector which detects light such as ultraviolet rays, infrared rays, and visible rays with high sensitivity and has excellent positional resolution and counting rate characteristics.

The optical detector 101 includes an optoelectric conversion section 2 for converting incident light into electrons and emitting them, a pixel type electrode 6 which is placed at a position facing the optoelectric conversion section 2 to amplify the electrons through gas within a chamber 7 and detect them, and a minus electrode 9 which is in contact with the periphery of the optoelectric conversion section 2 to be negative potential with respect to the pixel type electrode 6. The optical detector forms an electric field diverging from the optoelectric conversion section to the pixel type electrode, thereby allowing the electrons generated by the optoelectric conversion section to arrive at the pixel type electrode through similarly expansion with their positional information maintained.