An ion detection device for detecting: an ion that has passed through an ion separator which separates ions according to masses or mobilities of the ions; or an ion ejected from the ion separator, the ion detection device comprising: a) a conversion dynode disposed at a position outside of an extension line extending a central axis of a flow of injected ions such that a central axis of an ion collision face of the conversion dynode crosses the extension line of the central axis of the flow of injected ions, for converting, to an electron, the ion drawn by an electric field formed by the conversion dynode itself; b) an electron detector disposed opposite to the conversion dynode across the extension line of the central axis of the flow of the injected ions, for detecting the electron ejected from the conversion dynode; c) a shield electrode disposed between an injection position of the flow of the injected ions, and the conversion dynode as well as the electron detector, the shield electrode having: c1) a block wall disposed on the extension line of the central axis of the flow of the injected ions, configured to prevent a particle from passing, and c2) an electric field adjustment wall that extends from the block wall, formed in one of: a flat plane containing a straight line defining an acute angle with respect to the central axis of the flow of the injected ions as seen from the injection position of the flow of the injected ions in a plane containing both the central axis of the flow of the injected ions and the acentral axis of the ion collision face of the conversion dynode; a curved plane containing a curved line approximating the straight line; and a multi-facet plane approximating the curved plane, wherein the flat plane, the curved plane and the multi-facet plane approximate a curved equipotential plane of an electrical field formed by the conversion dynode in a state where no shield electrode is provided around a position where the shield electrode is located, and has an aperture or a cut portion configured to allow the ion moving to the conversion dynode to pass through; and d) a voltage applying section configured to apply a predetermined direct-current voltage to the shield electrode. a) a conversion dynode disposed at a position outside of an extension line extending a central axis of a flow of injected ions such that a central axis of an ion collision face of the conversion dynode crosses the extension line of the central axis of the flow of injected ions, for converting, to an electron, the ion drawn by an electric field formed by the conversion dynode itself; b) an electron detector disposed opposite to the conversion dynode across the extension line of the central axis of the flow of the injected ions, for detecting the electron ejected from the conversion dynode; c) a shield electrode disposed between an injection position of the flow of the injected ions, and the conversion dynode as well as the electron detector, the shield electrode having: c1) a block wall disposed on the extension line of the central axis of the flow of the injected ions, configured to prevent a particle from passing, and c2) an electric field adjustment wall that extends from the block wall, formed in one of: a flat plane containing a straight line defining an acute angle with respect to the central axis of the flow of the injected ions as seen from the injection position of the flow of the injected ions in a plane containing both the central axis of the flow of the injected ions and the acentral axis of the ion collision face of the conversion dynode; a curved plane containing a curved line approximating the straight line; and a multi-facet plane approximating the curved plane, wherein the flat plane, the curved plane and the multi-facet plane approximate a curved equipotential plane of an electrical field formed by the conversion dynode in a state where no shield electrode is provided around a position where the shield electrode is located, and has an aperture or a cut portion configured to allow the ion moving to the conversion dynode to pass through; and c1) a block wall disposed on the extension line of the central axis of the flow of the injected ions, configured to prevent a particle from passing, and c2) an electric field adjustment wall that extends from the block wall, formed in one of: a flat plane containing a straight line defining an acute angle with respect to the central axis of the flow of the injected ions as seen from the injection position of the flow of the injected ions in a plane containing both the central axis of the flow of the injected ions and the acentral axis of the ion collision face of the conversion dynode; a curved plane containing a curved line approximating the straight line; and a multi-facet plane approximating the curved plane, wherein the flat plane, the curved plane and the multi-facet plane approximate a curved equipotential plane of an electrical field formed by the conversion dynode in a state where no shield electrode is provided around a position where the shield electrode is located, and has an aperture or a cut portion configured to allow the ion moving to the conversion dynode to pass through; and d) a voltage applying section configured to apply a predetermined direct-current voltage to the shield electrode.