You know, I am almost positive I have seen that picture before on a joke website, somewhere around 4 years ago. So... yeah, I'm a bit suspicious that this is a hoax. Though I'm a polyglot, Japanese isn't one of the languages I can read (or speak) so I couldn't say if the PDF it links to is even relevant (or if that is actually a Japanese government website). Can anyone actually confirm if the linked PDF addresses "mobile suits"?
But... well I guess the biggest hint that this is a hoax is the fact that Japan IS allowed a human army. The Japanese Military participated for a while in Iraq, for example, and the Japanese Ground Self-Defense Force (their army) is their largest military branch. Thus, with a human army, the stated need for a gundam is bunk.
I certainly don't doubt that some governments would be interested in the technology, but that technology is also incredibly difficult to implement. Perhaps I am just not aware of it, but to my understanding no one has been able to make a bipedal robot that can walk on a flat surface at a respectable speed, much less over variable terrain. Seems like the Japanese government would start on a smaller scale if this were real.
Of course, General Electric tried to work on something like this back in 1965. The Hardiman Project was largely a failure, however.