A densitometer of the present invention comprises a main body having an opening and containing an internal liquid and an electrode in the opening, a permeable membrane sealing the opening, and a permeable membrane separated by a predetermined distance from the permeable membrane And an inflow / out portion which is an opening which communicates a gap between the permeable membrane and the water retaining portion and an external space of the body portion.本発明の濃度計は、開口部を有し前記開口部内に内部液及び電極を収容した本体部と、前記開口部を封止した透過膜と、前記透過膜から所定の距離離れて前記透過膜に対向する保水部と、前記透過膜及び前記保水部の間の隙間と、前記本体部の外部空間とを連通する開口である流出入部と、を備える。
