An air ion measuring device is provided which holds the air passage rate in an ion detector as constant as possible to provide for improved air ion measurement reliability, permits a size and thickness reduction and also a reduction of parts and cost of the ion detector, permits ready cleaning thereof, provides a measure for coping with static electricity, provides good visual recognition property in the air ion data display and displays data other than air ion data and error data. An ion detector structure is formed by disposing a charge collector electrode and repelling electrodes in the vicinity of opposite ends of the charge collector electrode on one side surface of an air passage, through which air is withdrawn from one end portion and exhausted from the other end portion, and disposing a further repelling electrode on the other side surface of the air passage.