An endoscope system according to the present invention is an endoscope system including an endoscope including an inserted portion and a connector portion, and a water-resistant cap configured to be airtightly installed at the connector portion. The connector portion includes a base portion, a sleeve portion, and an airtightness release portion provided at an end portion of the sleeve portion and configured to release an airtight state between the connector portion and the water-resistant cap. The water-resistant cap includes a cap main body and an abutting portion configured to abut on the sleeve portion. When the water-resistant cap is installed at the connector portion, the endoscope system takes any state of a first state where the abutting portion abuts on the sleeve portion at a side of the base portion with respect to the airtightness release portion to hold an airtightness between the water-resistant cap and the connector portion, and a second state where the abutting portion abuts on or faces the sleeve portion including the airtightness release portion to become non-airtight between the water-resistant cap and the connector portion.
