A CEM and an ion detector of one embodiment have a structure for enabling ion detection with higher sensitivity than the prior art. A channel electron multiplier includes a channel body, an input-side conductive layer, an output-side conductive layer, and an electrode. The channel body includes a channel, and a resistance layer and an electron emission layer formed on the channel's inner wall surface. The input-side conductive layer is provided on the channel body, and a part thereof extends into the tapered opening. The output-side conductive layer is provided on the tapered opening. The electrode has openings through which charged particles pass, and is disposed on an opposite side of the output end face to the input end face. The electrode and the input-side conductive layer are set to the same potential to eliminate the influence of an external electric field in the tapered opening.