The present embodiment relates to an ion detector provided with a structure for suppressing degradation over time in an electron multiplication mechanism in a multi-mode ion detector. The ion detector includes a dynode unit, a first electron detection portion including a semiconductor detector having an electron multiplication function, a second electron detection portion including an electrode, and a gate part. The first and second electron detection portions are capable of ion detection at different multiplication factors. The gate part includes at least a final-stage dynode as a gate electrode, and controls switching between passage and interruption of secondary electrons which are directed toward the first electron detection portion by adjusting a set potential of the gate electrode.