An endoscope reprocessor invention includes: a medicinal solution tank configured to store medicinal solution； a concentration measuring portion arranged in the medicinal solution tank so that a permeation membrane is submerged in the medicinal solution； a gas generating portion including a vaporizing portion configured to vaporize a part of the medicinal solution to generate gas and arranged at a position where the gas that floats upward in the medicinal solution is in contact with the permeation membrane； and a controlling portion connected to the concentration measuring portion and the gas generating portion and configured to perform first control to drive the concentration measuring portion in a state that the gas generating portion is stopped and second control to drive the concentration measuring portion in a state that the gas generating portion is driven.
