A cassette transfer unit associated with a cassette container having a cassette placed therein at a first position for transferring the cassette from and into the cassette container. The cassette transfer unit comprises a cassette chamber for receiving the cassette at a second position, and a carrying device provided in the cassette chamber for carrying the cassette from the cassette container into the cassette chamber and from the cassette chamber into the cassette container. The carrying device includes a first mechanism having a gripping element unit slidable toward and away from the cassette container for retracting the cassette from the first position toward the cassette chamber to a third position, and a second mechanism a holding arm unit slidable toward and away from the cassette container for retracting the cassette away from the cassette container from the third position to the second position.