Patent ID: 8921776

Claim:
An ion detecting device comprising: a casing having its inside under atmospheric pressure; an inlet through which ambient air is introduced into the casing that is placed under atmospheric pressure; a detection electrode, a voltage applying electrode that is placed opposite to the detection electrode in the casing, an electrode holding unit holding the detection electrode and the voltage applying electrode, and a wall made of the electrode holding unit and placed so as to close the direction which the ambient air is introduced in the casing, wherein the ambient air is ionized in an area between the detection electrode and the voltage applying electrode; a control unit that generates potential difference between the voltage applying electrode and the detection electrode, and by an electric field created between the voltage applying electrode and the detection electrode, separates the ambient air introduced through the inlet into ions in the casing; and a current detecting unit connected to the detection electrode and that detects current based on the ions collected by the detection electrode; wherein the electrode holding unit is made of material with a water absorption rate of 0.4 or smaller.