There is provided an electrolyte measuring device that can decrease a liquid amount used for measurement, in which stable sealing can be provided in connecting passages of ion selective electrodes to each other with no gap, while maintaining high measurement accuracy of an existing ion selective electrode, and a residing sample liquid can be greatly decreased. In a flow-type ion selective electrode, a sealing member is used, which can be brought into intimate contact with a passage connecting unit to near a passage hole. A gap regulating member is provided to keep a gap between the electrodes constant and to prevent the sealing member from being excessively pressed. An electrode case has a structure suitable for the sealing member for allowing the alignment and holding of the sealing member.
