The present embodiment relates to a charged-particle detector, etc. provided with a structure for effectively suppressing ion feedbacks under a low-vacuum environment. In order to capture the residual-gas ions, which are generated by collisions between the electrons output from a MCP unit 200 and residual-gas molecules, by a second electrode 400, which is electrically insulated from a first electrode 300, which is mainly for capturing electrons, the potential of the first electrode 300 is set to be higher than an output-side potential of the MCP unit 200, and, on the other hand, the potential of the second electrode 400 is set to be lower than the output-side potential of the MCP unit 200. As a result, the ion feedbacks to the MCP unit 200 are effectively suppressed.