An ionizer is formed by coupling a fan unit provided with a discharge electrode and a fan and a control unit provided with an indicator and an adjuster to each other, and both units are changeable between a normal coupling condition, where both are directed in the same direction, and an opposite coupling condition, where they are directed in opposite directions to each other, and in addition, a power/signal arrangement of the connection terminals of the separate connector is bilaterally symmetrical such that same power and signals ale transmitted and received between the separate connectors of both units connected to each other in either coupling condition of aforementioned both units.