A device for measuring a tension of a cell structure containing muscle cells includes a first and a second gel adaptor holder. The first gel adaptor holder includes a frame member and a first gel holding portion which is disposed protrudingly from a part of an inner surface of the frame member for fixing one end of a gel. The second gel adaptor holder includes a second gel holding portion that fixes another end of the gel, and connecting members connected with the second gel holding portion. A kit including the device, a substrate and a gel forming cover. The substrate includes a pair of gel shaping convex parts fitted along the inner surface of the frame member. The gel forming cover includes a surface parallel to a gel contacting surface of the substrate, in order to form an upper surface of the gel.