I think this is actually a "Fukuro Shinai" or "Bag Shinai" though it looks not the same as most others I`ve seen do. A Fukuro Shinai is a Shinai which is clothed within leather.
More common Shinai are for example here: http://kendo.tozando.com/shinai/s136.html
(As you can see its bamboparts have the shape of the normal shinai)
or here: http://at80.jp/shinai/sankou/shinai_sankou1.html
(Here is what can be under the "bag")
Oh, I searched for a further Photo of a Fukuro Shinai made by Tim Bathurst, who makes (under Grandmaster Hatsumi´s authority) the training weapons for the Bujinkan. I know they are really good, but unfortunately, the Site is closed up to August. But I found another interesting link: http://at80.jp/shinai/shinai_histry.html
Here`are Fukuro Shinai of Yagyu-Style: http://www.bujindesign.com/weapons_bamboo.html
[This message has been edited by Wilf (edited 03-09-2005).]