A square cylindrical drift cell (10) is formed by bonding together four resistive film layer members in which a resistive film layer (12) of a specified film thickness is formed by a coating method or evaporation method on a plate member (11) consisting of an insulating material such as alumina. Impressing respectively predetermined voltages on the resistive film layer (12) at both ends of this drift cell (10) from a drift voltage generating unit (8) forms an accelerating electric field having a linear potential gradient along the center axis (C) in a desolventizing region (2) and drift region (3) in the drift cell (10). Ions drift due to this accelerating electric field and are separated from each other in accordance with the mobility of the ions. Since it is possible to manufacture the resistive film layer member at a low cost, and the drift cell (10) assembly process is simple, it is possible to provide the drift cell (10) at low cost. Also, since the film thickness uniformity of the resistive film layer (
