Provided is a cover used for a thermostatic apparatus including an inner chamber enclosed with a plurality of walls and a temperature/humidity controller for controlling temperature and humidity in the inner chamber. The cover forms a space with a wall of the plurality of walls by being attached to the wall so as to cover a hole provided in the wall. The cover includes a opening through which a cord-shaped body passes, the cord-shaped body extending from the outside of the inner chamber to the inside thereof through the hole, a peripheral part being in hermetic contact with the wall; a contact part being in hermetic contact with the cord-shaped body in the opening; and a sealant being in hermetic contact with the hole. The cord-shaped body is led through the sealant in hermetic state, and a part of the cord-shaped body is housed in the space.