Acridinium compounds represented by the general formula (I) where A is an intervening group which does not have activity for binding with a specific binding substance, Z is a labelling active group which has activity for binding with a specific binding substance, R¹ is a halogen atom, an alkyl group or an aryl group; R², R³, R⁴ and R⁵ are each a hydrogen atom, an alkyl group, an aryl group, an alkoxy group, a nitro group, a halogen atom or a carbonyl group, and Y is a counter ion. The acridinium compounds may form conjugates with specific binding substances. The acridinium compounds have high emission efficiency and stability and, hence, are useful as chemiluminescence labelling agents.