The present invention relates to an MCP unit or the like having a structure intended to achieve a desired
time response characteristic, without depending on a limitation imposed by a channel
diameter of MCP. The MCP unit comprises the MCP for releasing
secondary electrons internally multiplied in response to incidence of charged particles, an
anode arranged in a position where the
secondary electrons reach, and an acceleration
electrode arranged between the MCP and the
anode. In particular, the acceleration
electrode includes a plurality of openings which permit passing of the
secondary electrons migrating from the MCP toward the
anode. Further, the acceleration
electrode is arranged such that the
shortest distance B between the acceleration electrode and the anode is longer than the
shortest distance A between the MCP and the acceleration electrode. Thus, an FWHM of a detected peak appearing in response to the incidence of the charged particles is remarkably shortened.