A concentration meter of the invention includes: a main body section including an opening portion, and an internal liquid and an electrode housed in the opening portion； a permeation membrane that seals the opening portion； a water-holding section that is opposed to the permeation membrane with a predetermined distance separated from the permeation membrane； and an inflow/outflow section which is an opening that allows a clearance between the permeation membrane and the water-holding section to communicate with a space outside the main body section.
