The present invention relates to a reliable water swapping device comprising: a container which has a space therein and has an open top； a joining unit which is formed to be extended from the bottom of the container toward the upside, has the penetrated inside, and includes an inlet hole, capable of communicating with the inside, on a side surface； and an adjusting means which is formed on the joining unit, and adjusts the amount of water entering the inside of the container through the inlet hole by adjusting a degree of closeness of the inlet hole formed on the joining unit. A degree of closeness of the inlet hole of the joining unit formed on the container, accommodating living organisms which have been parceled out, can be adjusted as a user desires by operating the adjusting means. Therefore, the amount of water (a flow volume) entering through the inlet hole can be adjusted to be proper to a kind of the living organisms. Consequently, a survival rate of the living organisms is increased by preventing death of the living organisms caused by shock and, at the same time, the reliable water swapping device can provide convenience in use to the user as time for swapping water can be reduced. Moreover, when the container, accommodating the living organisms, is floated on an aquarium for swapping water, water in the aquarium slowly enters through the inlet hole of the joining unit and then water swapping is finished. When water is filled in the container, the container naturally sinks and the living organisms, accommodated by the container, enter water in the aquarium. Therefore, unlike an existing method, the user does not need to separately placing living organisms into water in an aquarium. Accordingly, a water swapping process can be easy and convenient, and convenience in use can be provided to the user as quality and the temperature of water can be adjusted at the same time. In addition, the reliable water swapping device has a very hygienic effect when compare
