A ventilation device comprises: a body, a fan disposed In the body, and an adapter connected with an air outlet of the body. Two or more pipe coupling parts are disposed in sequence from a side of an air Inlet of the adapter to a side of an air outlet of the adapter, and each pipe coupling part is provided with a protruding circular ring with a diameter larger than that of the respective pipe coupling part at a root thereof. An air guide structure Is disposed in the adapter, a pipe is fitted over the pipe coupling part and Is abutted against the protruding circular ring located at the root to be fixed, and the air guide structure Is engaged to an inside of the protruding circular ring of the adapter.